U.S. patent application number 13/514752 was filed with the patent office on 2012-09-27 for exhaust gas purification system for an internal combustion engine.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Bungo Kawaguchi, Satoshi Kobayakawa, Tomihisa Oda, Tomomi Onishi, Masaaki Sato, Takeru Shirasawa.
Application Number | 20120240557 13/514752 |
Document ID | / |
Family ID | 44145219 |
Filed Date | 2012-09-27 |
United States Patent
Application |
20120240557 |
Kind Code |
A1 |
Kawaguchi; Bungo ; et
al. |
September 27, 2012 |
EXHAUST GAS PURIFICATION SYSTEM FOR AN INTERNAL COMBUSTION
ENGINE
Abstract
An exhaust gas purification system for an internal combustion
engine, which is provided with: a selective reduction type catalyst
arranged in an exhaust passage of the internal combustion engine; a
low pressure EGR mechanism that is equipped with a low pressure EGR
passage for introducing a part of an exhaust gas flowing through a
portion of the exhaust passage downstream of a turbine of a
centrifugal supercharger to a portion of an intake passage upstream
of a compressor as a low pressure EGR gas, and a low pressure EGR
valve for changing a channel cross section of the low pressure EGR
passage; a supply device.
Inventors: |
Kawaguchi; Bungo;
(Susono-shi, JP) ; Oda; Tomihisa; (Numazu-shi,
JP) ; Onishi; Tomomi; (Susono-shi, JP) ; Sato;
Masaaki; (Susono-shi, JP) ; Kobayakawa; Satoshi;
(Susono-shi, JP) ; Shirasawa; Takeru; (Susono-shi,
JP) |
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi, Aichi
JP
|
Family ID: |
44145219 |
Appl. No.: |
13/514752 |
Filed: |
December 8, 2009 |
PCT Filed: |
December 8, 2009 |
PCT NO: |
PCT/JP2009/070528 |
371 Date: |
June 8, 2012 |
Current U.S.
Class: |
60/278 |
Current CPC
Class: |
Y02T 10/12 20130101;
F02D 41/0065 20130101; F01N 3/20 20130101; F02M 26/05 20160201;
F02M 26/08 20160201; F02B 29/0406 20130101; F01N 3/2013 20130101;
F02M 26/23 20160201; F02D 41/005 20130101; F02M 26/15 20160201;
F02B 37/22 20130101; Y02T 10/47 20130101; F01N 2610/02 20130101;
F01N 2610/1453 20130101; F02M 26/36 20160201; F01N 2240/36
20130101; F01N 13/009 20140601; Y02T 10/40 20130101; F02D 41/126
20130101; F02M 26/10 20160201; F02M 26/06 20160201; F01N 3/208
20130101; F01N 2240/40 20130101; Y02T 10/24 20130101; Y02T 10/26
20130101 |
Class at
Publication: |
60/278 |
International
Class: |
F02M 25/07 20060101
F02M025/07; F01N 3/24 20060101 F01N003/24 |
Claims
1. An exhaust gas purification system for an internal combustion
engine comprising: a selective reduction type catalyst that is
arranged in an exhaust passage of the internal combustion engine; a
low pressure EGR mechanism that is equipped with a low pressure EGR
passage which serves to introduce a part of an exhaust gas flowing
through a portion of the exhaust passage downstream of a turbine of
a centrifugal supercharger to a portion of an intake passage
upstream of a compressor as a low pressure EGR gas, and a low
pressure EGR valve which serves to change a channel cross section
of said low pressure EGR passage; a supply device which serves to
supply an ammonia derived compound to said selective reduction type
catalyst, and is arranged in such a manner that the ammonia derived
compound is able to be supplied into the exhaust passage at a
location upstream of a connection portion of said low pressure EGR
passage; and control unit for causing said supply device to supply
the ammonia derived compound therefrom when said low pressure EGR
valve is in a valve open state.
2. The exhaust gas purification system for an internal combustion
engine according to claim 1, further comprising: obtaining unit for
obtaining a value which is correlated with an amount of acidic
substances existing in a path of the low pressure EGR gas; wherein
said control unit makes the amount of the ammonia derived compound
supplied from said supply device larger in cases where the value
obtained by said obtaining unit is large, in comparison with the
case where it is small.
3. The exhaust gas purification system for an internal combustion
engine according to claim 1, further comprising: detection unit for
detecting the temperature of the low pressure EGR gas; wherein said
control unit makes an amount of the ammonia derived compound
supplied from said supply device larger in cases where the
temperature detected by said detection unit is higher than a
predetermined reference temperature, in comparison with the case
where the detected temperature is lower than the predetermined
reference temperature.
4. The exhaust gas purification system for an internal combustion
engine according to claim 1, further comprising: heating unit for
heating the low pressure EGR gas; wherein said control unit
operates said heating unit when the ammonia derived compound is
caused to be supplied from said supply device.
5. The exhaust gas purification system for an internal combustion
engine according to claim 4, wherein said selective reduction type
catalyst is arranged in a portion of the exhaust passage at the
upstream side of a connection portion of said low pressure EGR
passage; and said heating unit heats said selective reduction type
catalyst.
6. The exhaust gas purification system for an internal combustion
engine according to claim 4, wherein said selective reduction type
catalyst is arranged in a portion of the exhaust passage at the
upstream side of a connection portion of said low pressure EGR
passage; and said heating unit heats the exhaust gas before flowing
into said selective reduction type catalyst.
7. The exhaust gas purification system for an internal combustion
engine according to claim 1, wherein said selective reduction type
catalyst is arranged in a portion of the exhaust passage at the
upstream side of a connection portion of said low pressure EGR
passage.
8. The exhaust gas purification system for an internal combustion
engine according to claim 7, wherein when said low pressure EGR
valve is in a valve open state, said control unit causes said
supply device to supply an amount of the ammonia derived compound
more than that which is able to be adsorbed by said selective
reduction type catalyst.
9. The exhaust gas purification system for an internal combustion
engine according to claim 1, wherein said selective reduction type
catalyst is arranged in a portion of the exhaust passage at the
downstream side of a connection portion of said low pressure EGR
passage.
10. The exhaust gas purification system for an internal combustion
engine according to claim 9, further comprising: a dispersion plate
that is arranged in a portion of the exhaust passage at the
downstream side of the connection portion of said low pressure EGR
passage and at the upstream side of said selective reduction type
catalyst, and disperses the ammonia derived compound supplied from
said supply device.
11. The exhaust gas purification system for an internal combustion
engine according to claim 9, wherein said control unit makes the
amount of the ammonia derived compound supplied from said supply
device larger in cases where an amount of the low pressure EGR gas
flowing through said low pressure EGR passage is large, in
comparison with the case where it is small.
12. The exhaust gas purification system for an internal combustion
engine according to claim 1, further comprising: a high pressure
EGR mechanism that is equipped with a high pressure EGR passage
which serves to introduce a part of the exhaust gas flowing through
a portion of the exhaust passage at the upstream side of the
turbine of said centrifugal supercharger to a portion of the intake
passage at the downstream side of the compressor as a high pressure
EGR gas, and a high pressure EGR valve which serves to change a
channel cross section of said high pressure EGR passage; and
calculation unit for calculating an amount of the ammonia derived
compound flowing through said low pressure EGR passage; wherein
said control unit corrects a ratio between a flow rate of the low
pressure EGR gas and a flow rate of the high pressure EGR gas
according to a result of the calculation of said calculation
unit.
13. The exhaust gas purification system for an internal combustion
engine according to claim 12, wherein in cases where the result of
the calculation of said calculation unit is less than a target
amount, said control unit corrects the degree of opening of said
low pressure EGR valve to an open side, and at the same time
corrects the degree of opening of said high pressure EGR valve to a
closed side.
14. The exhaust gas purification system for an internal combustion
engine according to claim 12, wherein in cases where the result of
the calculation of said calculation unit is larger than a target
amount, said control unit corrects the degree of opening of said
low pressure EGR valve to a closed side, and at the same time
corrects the degree of opening of said high pressure EGR valve to
an open side.
15. The exhaust gas purification system for an internal combustion
engine according to claim 1, wherein said control unit carries out
supply processing which is processing to cause said low pressure
EGR valve to open so that the ammonia derived compound is made to
be supplied from said supply device, when deceleration fuel cut-off
control of the internal combustion engine is carried out.
16. The exhaust gas purification system for an internal combustion
engine according to claim 15, further comprising: an exhaust
throttle valve that is arranged in a portion of the exhaust passage
at the downstream side of the connection portion of said low
pressure EGR passage and at the downstream side of said selective
reduction type catalyst, and changes a channel cross section of the
exhaust passage; wherein said control unit causes said exhaust gas
throttle valve to close at the time of carrying out said supply
processing.
17. The exhaust gas purification system for an internal combustion
engine according to claim 15, wherein said control unit makes an
amount of low pressure EGR gas to be introduced into the intake
passage for a predetermined period of time after termination of the
deceleration fuel cut-off control smaller in cases where said
supply processing has been carried out, in comparison with the case
where said supply processing has not been carried out.
18. The exhaust gas purification system for an internal combustion
engine according to claim 17, further comprising: a high pressure
EGR mechanism that is equipped with a high pressure EGR passage
which serves to introduce a part of the exhaust gas flowing through
a portion of the exhaust passage at the upstream side of the
turbine of said centrifugal supercharger to a portion of the intake
passage at the downstream side of the compressor as a high pressure
EGR gas, and a high pressure EGR valve which serves to change a
channel cross section of said high pressure EGR passage; wherein
said control unit corrects the degree of opening of said high
pressure EGR valve to an open side after said predetermined period
of time has elapsed.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust gas purification
system for an internal combustion engine, and in particular to a
technique which serves to suppress the component parts of an intake
system from being corroded by an EGR (Exhaust Gas Recirculation)
gas.
BACKGROUND ART
[0002] In recent years, there has been known a low pressure EGR
device (LPL-EGR system) which serves to introduce a part of an
exhaust gas flowing downstream of a turbine of a centrifugal
supercharger into intake air upstream of a compressor thereof. In
an internal combustion engine provided with an LPL-EGR system, when
condensed water existing in a path of an EGR gas comes in contact
with the EGR gas, the hydrogen ion exponent or power of hydrogen
ions (pH) of the condensed water may be dropped (or strongly
acidized or oxidized).
[0003] As a result, there is a possibility that the above-mentioned
condensed water and/or substances evaporated from the condensed
water may cause chemical changes on component parts such as a
compressor, an intercooler, and so on. On the other hand, there has
also been proposed a technique in which an addition valve for
adding a neutralizing agent is arranged in an intake passage at a
location upstream of a compressor (for example, see a first patent
document).
PRIOR ART DOCUMENTS
Patent Documents
[0004] Patent Document 1: Japanese Patent Application Laid-Open No.
2008-144633 [0005] Patent Document 2: Japanese Patent Application
Laid-Open No. 09-324706 [0006] Patent Document 3: Japanese Patent
Application Laid-Open No. 2009-92005 [0007] Patent Document 4:
Japanese Patent Application Laid-Open No. 2009-85011 [0008] Patent
Document 5: Japanese Patent Application Laid-Open No. 11-82182
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0009] According to the above-mentioned conventional technique,
however, it is necessary to newly add the neutralizing agent
addition valve, thus giving rise to a possibility that an increase
in the number of component parts and a reduction in vehicle
mountability may be caused.
[0010] The present invention has been made in view of the
above-mentioned actual circumstances, and has for its object to
provide a technique which is capable of suppressing chemical
changes in component parts arranged in a path of an EGR gas, while
suppressing an increase in the number of parts in an exhaust gas
purification system for an internal combustion engine provided with
a low pressure EGR device.
Means for Solving the Problem
[0011] In order to solve the above-mentioned problems, the present
invention resides in an exhaust gas purification system for an
internal combustion engine which is provided with a low pressure
EGR mechanism for introducing a part of an exhaust gas (a low
pressure EGR gas) from an exhaust passage downstream of a turbine
of a centrifugal supercharger to an intake passage upstream of a
compressor thereof, wherein an ammonia derived compound is supplied
to a low pressure EGR gas passage by making use of a supply device
which serves to supply the ammonia derived compound to a selective
reduction type catalyst.
[0012] Specifically, an exhaust gas purification system for an
internal combustion engine of the present invention comprises:
[0013] a selective reduction type catalyst that is arranged in an
exhaust passage of the internal combustion engine;
[0014] a low pressure EGR mechanism that is equipped with a low
pressure EGR passage which serves to introduce a part of an exhaust
gas flowing through a portion of the exhaust passage downstream of
a turbine of a centrifugal supercharger to s portion of an intake
passage upstream of a compressor as a low pressure EGR gas, and a
low pressure EGR valve which serves to change a channel cross
section of said low pressure EGR passage;
[0015] a supply device that serves to supply an ammonia derived
compound to said selective reduction type catalyst, and is arranged
in such a manner that the ammonia derived compound is able to be
supplied into the exhaust passage at a location upstream of a
connection portion of said low pressure EGR passage; and
[0016] control unit for causing said supply device to supply the
ammonia derived compound therefrom when said low pressure EGR valve
is in a valve open state.
[0017] According to such an invention, a part of the ammonia
derived compound supplied from the supply device will be supplied
to the intake passage by way of the low pressure EGR passage. For
that reason, acidic substances (e.g., condensed water, substances
evaporated from condensed water, etc.) which exist in a path of the
low pressure EGR gas (e.g., the low pressure EGR passage, the
intake passage, the compressor, an intercooler, etc.) are
neutralized by the ammonia derived compound.
[0018] Further, as the supply device, there is used an existing
device which is provided in order to supply the ammonia derived
compound as a reducing agent to the selective reduction type
catalyst, and hence, it becomes possible to suppress chemical
changes in the component parts existing in the path of the low
pressure EGR gas, while suppressing an increase in the number of
component parts.
[0019] The exhaust gas purification system for an internal
combustion engine of the present invention may be further provided
with obtaining unit for obtaining a value which is correlated with
an amount of acidic substances existing in the path of the low
pressure EGR gas. In that case, the control unit may make an amount
of ammonia derived compound to be supplied larger in cases where
the amount or value obtained by the obtaining unit is large, in
comparison with the case where it is small.
[0020] When the amount of supply of the ammonia derived compound is
adjusted in the manner as stated above, it becomes possible to
neutralize the acidic substances existing in the path of the low
pressure EGR gas in a more reliable manner. Here, note that the
control unit may perform control in such a manner that the lower
the hydrogen ion exponent (pH) of the acidic substances existing in
the path of the low pressure EGR gas, the more the amount of supply
of the ammonia derived compound becomes.
[0021] The exhaust gas purification system for an internal
combustion engine according to the present invention may be further
provided with detection unit for detecting the temperature of the
low pressure EGR gas. In that case, the control unit may make the
amount of supply of the ammonia derived compound larger when the
temperature detected by the detection unit is higher than a
predetermined reference temperature, than when it is lower than the
predetermined reference temperature. The reference temperature
referred to herein is, for example, a lower limit value of a
temperature range in which the ammonia derived compound can be
hydrolyzed.
[0022] When the ammonia derived compound is hydrolyzed, there are
produced compounds with high acid neutralization ability, such as
ammonia (NH.sub.3). For that reason, if the amount of supply of the
ammonia derived compound is adjusted according to the temperature
of the low pressure EGR gas, a large amount of ammonia derived
compound will not be supplied when the acid neutralization ability
is low. As a result, the situation where the amount of consumption
of the ammonia derived compound increases unnecessarily is
avoided.
[0023] Here, note that the control unit may stop the operation of
the supply device the amount of supply of the ammonia derived
compound (i.e., may stop the supply of the ammonia derived
compound) in cases where the temperature detected by the detection
unit is lower than said predetermined reference temperature. In
that case, the amount of consumption of the ammonia derived
compound can be suppressed to a minimum.
[0024] The exhaust gas purification system for an internal
combustion engine according to the present invention may be further
provided with heating unit for heating the low pressure EGR gas. In
that case, the control unit may operate the heating unit when the
ammonia derived compound is caused to be supplied from the supply
device. If the heating unit is caused to operate in this manner, it
will be possible to hydrolyze the ammonia derived compound even in
cases where the temperature of the exhaust gas is low. As a result,
an opportunity to neutralize the acidic substances existing in the
path of the low pressure EGR gas will increase.
[0025] Here, note that in cases where the selective reduction type
catalyst is arranged in a portion of the exhaust passage at the
upstream side of the connection portion of the low pressure EGR
passage, the heating unit may heat the selective reduction type
catalyst, or may heat the exhaust gas before flowing into the
selective reduction type catalyst.
[0026] According to such a heat method, it becomes possible to heat
the selective reduction type catalyst, too, in addition to the
ammonia derived compound supplied from the supply device. The
selective reduction type catalyst has the property of becoming
difficult to adsorb the ammonia derived compound, when subjected to
high temperatures.
[0027] Accordingly, if the selective reduction type catalyst is
heated at the time when the supply device supplies the ammonia
derived compound, almost all of the ammonia derived compound
supplied from the supply device will come to pass through the
selective reduction type catalyst. As a result, it becomes easy to
adjust the amount of the ammonia derived compound flowing into the
low pressure EGR gas passage.
[0028] However, a case can also be assumed where the selective
reduction type catalyst has adsorbed the ammonia derived compound
at the time when the ammonia derived compound is supplied to the
path of the low pressure EGR gas. In such a case, if the heating
unit heats the selective reduction type catalyst in a direct or
indirect manner, the ammonia derived compound released from the
selective reduction type catalyst, in addition to the ammonia
derived compound supplied from the supply device, will also be
introduced to the path of the low pressure EGR gas. As a result, in
cases where the selective reduction type catalyst is heated, the
amount of the ammonia derived compound introduced to the path of
the low pressure EGR gas increases more than in cases where the
selective reduction type catalyst is not heated.
[0029] Accordingly, it is preferable that the amount of the ammonia
derived compound to be supplied from the supply device be made an
amount which is deducted by an amount of the ammonia derived
compound which has been adsorbed by the selective reduction type
catalyst. In that case, it is possible to avoid the situation where
the ammonia derived compound introduced into the path of the low
pressure EGR gas becomes excessive, and at the same time to
suppress the amount of the ammonia derived compound to be supplied
from the supply device to a minimum level as required. Here, note
that the amount of the ammonia derived compound which has been
adsorbed by the selective reduction type catalyst can be calculated
by using, as parameters, the amount of supply of the ammonia
derived compound, the bed temperature of the selective reduction
type catalyst, etc.
[0030] Here, as the heating unit, there can be used a heater that
serves to convert electrical energy into thermal or heat energy.
However, in a system which is not provided with the heater, it is
also possible to heat the ammonia derived compound by means of the
following methods, i.e., a method of decreasing the degree of
opening of an intake throttle valve, a method of decreasing the
degree of opening of an exhaust throttle valve, a method of
expanding the capacity of a variable capacity type turbo charger
(i.e., increasing the degree of opening of a nozzle vane), a method
of increasing the amount of EGR gas, a method of retarding the
ignition timing of fuel in the internal combustion engine, and so
on.
[0031] In addition, in the construction in which the selective
reduction type catalyst is arranged in a portion of the exhaust
passage at the upstream side of the connection portion of the low
pressure EGR passage, the ammonia derived compound supplied from
the supply device will be hydrolyzed by the selective reduction
type catalyst. For this reason, in the construction in which the
selective reduction type catalyst is arranged at the upstream side
of the connection portion of the low pressure EGR passage, there is
no need to provide heating unit as referred to above.
[0032] However, in a construction in which no heating unit is
provided, there will be a possibility that the ammonia derived
compound supplied from the supply device may be adsorbed to the
selective reduction type catalyst. For that reason, in case where
the ammonia derived compound is supplied to the path of the low
pressure EGR gas, it is necessary to supply an amount of ammonia
derived compound more than the amount of the ammonia derived
compound which can be adsorbed by the selective reduction type
catalyst.
[0033] Therefore, when it is necessary to supply the ammonia
derived compound to the path of the low pressure EGR gas, the
control unit may cause the supply device to supply an amount of the
ammonia derived compound more than that which is able to be
adsorbed by the selective reduction type catalyst.
[0034] In the exhaust gas purification system for an internal
combustion engine according to the present invention, the selective
reduction type catalyst may be arranged in a portion of the exhaust
passage at the downstream side of the connection portion of the low
pressure EGR passage. In that case, because the selective reduction
type catalyst becomes resistant to the flow of the exhaust gas, the
pressure of the exhaust gas at the upstream side of the selective
reduction type catalyst becomes high. For this reason, the ammonia
derived compound can be supplied to the low pressure EGR passage,
without throttling the degree of opening of the exhaust throttle
valve to a substantial extent. As a result, it is possible to
neutralize the acidic substances in the path of the low pressure
EGR gas, without increasing the back pressure acting on the
internal combustion engine to a large extent.
[0035] Here, note that in the construction in which the selective
reduction type catalyst is arranged in a portion of the exhaust
passage at the downstream side of the connection portion of the low
pressure EGR passage, in cases where a catalyst (e.g., an oxidation
catalyst, etc.) is arranged at the upstream side of the connection
portion of the low pressure EGR passage, too, it is desirable that
a pressure loss of that catalyst be made smaller than a pressure
loss of the selective reduction type catalyst.
[0036] In addition, in the construction in which the selective
reduction type catalyst is arranged in a portion of the exhaust
passage at the downstream side of the connection portion of the low
pressure EGR passage, in cases where a dispersion plate for
dispersing the ammonia derived compound supplied from the supply
device is arranged in the exhaust passage, the dispersion plate may
be arranged in the portion of the exhaust passage at the downstream
side of the connection portion of the low pressure EGR passage.
[0037] In that case, the exhaust gas pressure in the connection
portion of the low pressure EGR passage is increased due to the
pressure loss of the selective reduction type catalyst and the
pressure loss of the dispersion plate. As a result, the ammonia
derived compound supplied from the supply device will become
further easy to flow into the low pressure EGR passage.
[0038] Here, note that in the construction in which the selective
reduction type catalyst is arranged in the portion of the exhaust
passage at the downstream side of the connection portion of the low
pressure EGR passage, the control unit may make the amount of the
ammonia derived compound supplied from the supply device larger in
cases where an amount of the low pressure EGR gas flowing through
the low pressure EGR passage is large, in comparison with the case
where it is small.
[0039] The amount of the ammonia derived compound flowing into the
low pressure EGR passage becomes more when the amount of the low
pressure EGR gas is large, than when it is small, and at the same
time, the amount of the ammonia derived compound flowing into the
selective reduction type catalyst becomes less when the amount of
the low pressure EGR gas is large, than when it is small. For that
reason, the ammonia derived compound supplied to the selective
reduction type catalyst may become short or insufficient.
[0040] In contrast to this, if ammonia (NH.sub.3) is supplied from
the supply device in a larger amount when the amount of low
pressure EGR gas is large, than when it is small, it will be
possible to avoid the situation where the ammonia derived compound
supplied to the selective reduction type catalyst becomes short or
insufficient. As a result, it will become possible to neutralize
the acidic substances existing in the path of the low pressure EGR
gas, without decreasing the purification ability of the selective
reduction type catalyst.
[0041] In cases where the internal combustion engine to which the
present invention is applied is provided with a low pressure EGR
mechanism and a high pressure EGR mechanism, the exhaust gas
purification system for an internal combustion engine according to
the present invention may be further provided with calculation unit
for calculating an amount of the ammonia derived compound flowing
through the low pressure EGR passage. In that case, the control
unit may correct a ratio between a flow rate of the low pressure
EGR gas and a flow rate of the high pressure EGR gas according to a
result of the calculation of the calculation unit. Here, note that
the high pressure EGR mechanism referred to herein is a mechanism
that is provided with a high pressure EGR passage which serves to
introduce a part of the exhaust gas flowing through a portion of
the exhaust passage at the upstream side of the turbine of the
centrifugal supercharger to a portion of the intake passage at the
downstream side of the compressor as a high pressure EGR gas, and a
high pressure EGR valve which serves to change a channel cross
section of said high pressure EGR passage.
[0042] According to such a construction, in cases where the result
of the calculation of the calculation unit is less than a target
amount, the control unit can cause the amount of low pressure EGR
gas to increase, without changing the amount of EGR gas (the total
amount of the low pressure EGR gas and the high pressure EGR gas)
introduced into the internal combustion engine, by correcting the
degree of opening of the low pressure EGR valve to an open side (in
an increasing direction) and at the same time correcting the degree
of opening of the high pressure EGR valve to a closed side (in a
decreasing direction). As a result, it is possible to increase the
amount of the ammonia derived compound flowing through the low
pressure EGR gas passage to a target value.
[0043] On the other hand, in cases where the result of the
calculation of the calculation unit is more than the target amount,
the control unit can cause the amount of low pressure EGR gas to
decrease, without changing the amount of EGR gas introduced into
the internal combustion engine, by correcting the degree of opening
of the low pressure EGR valve to a closed side and at the same time
correcting the degree of opening of the high pressure EGR valve to
an open side. As a result, it is possible to decrease the amount of
the ammonia derived compound flowing through the low pressure EGR
gas passage to the target value.
[0044] The control unit of the present invention may carry out
supply processing which is processing to cause the low pressure EGR
valve to open so that the ammonia derived compound is made to be
supplied from the supply device, at the time when deceleration fuel
cut-off control of the internal combustion engine is carried out.
In that case, it becomes possible to adjust the amount of low
pressure EGR gas, without affecting the combustion state of the
internal combustion engine. As a result, it also becomes possible
to adjust the amount of the ammonia derived compound flowing
through the low pressure EGR gas passage, without affecting the
combustion state of the internal combustion engine.
[0045] Here, note that in cases where the above-mentioned supply
processing is carried out, the control unit may close an exhaust
throttle valve, which is arranged in a portion of the exhaust
passage at the downstream side of the connection portion of the low
pressure EGR passage and at the downstream side of the selective
reduction type catalyst. In that case, all the amount of the
ammonia derived compound supplied from the supply device will flow
into the low pressure EGR passage. As a result, it is possible to
neutralize the acidic substances by means of a minimum amount of
the ammonia derived compound. Moreover, it is also possible to
suppress the situation where the ammonia derived compound is
released into the atmospheric air.
[0046] In addition, the control unit may make an amount of the low
pressure EGR gas to be introduced into the intake passage for a
predetermined period of time after termination of the deceleration
fuel cut-off control smaller in cases where the above-mentioned
supply processing has been carried out, in comparison with the case
where the supply processing has not been carried out.
[0047] In cases where the above-mentioned supply processing has not
been carried out, the inside of the path of the low pressure EGR
gas will be filled with air. On the other hand, in cases where the
above-mentioned supply processing has been carried out, the inside
of the path of the low pressure EGR gas will be filled with the low
pressure EGR gas.
[0048] Accordingly, in cases where the above-mentioned supply
processing has been carried out, if the amount of low pressure EGR
gas after the termination of the deceleration fuel cut-off control
is made equal to that in cases where the supply processing has not
been carried out, there will be a possibility that the amount of
oxygen introduced into the internal combustion engine may become
too small.
[0049] Consequently, in cases where the above-mentioned supply
processing has been carried out, if the amount of low pressure EGR
gas for the predetermined period of time after the termination of
the deceleration fuel cut-off control is made smaller in comparison
with the case where the supply processing has not been carried out,
it is possible to avoid the situation where the amount of oxygen
introduced into the internal combustion engine becomes too
small.
[0050] Here, note that the above-mentioned predetermined period of
time corresponds to a period of time taken until the low pressure
EGR gas existing in the intake passage at the downstream side of
the connection portion of the low pressure EGR passage has been
scavenged with fresh air (air) (in other words, a period of time
taken for the concentration of oxygen in the intake passage at the
downstream side of the connection portion of the low pressure EGR
passage to rise to a concentration which has been beforehand set).
The period of time taken until the low pressure EGR gas existing in
the intake passage has been scavenged can be calculated by using,
as parameters, the volume of a path extending from the connection
portion of the low pressure EGR passage to the internal combustion
engine, and the number of engine revolutions per unit time (in
other words, the amount of gas which is taken in per unit time by
the internal combustion engine).
[0051] However, it is necessary to cause the amount of low pressure
EGR gas to increase up to an ordinary amount (a target amount of
low pressure EGR gas in cases where the above-mentioned supply
processing has not been carried out) after the elapse of the
above-mentioned predetermined period of time, it will take some
period of time (a transport delay of the low pressure EGR gas)
until the low pressure EGR gas taken into the low pressure EGR
passage from the exhaust passage reaches the internal combustion
engine. For that reason, there will be a possibility that the
amount of the low pressure EGR gas introduced into the internal
combustion engine after the elapse of the predetermined period of
time may become short or insufficient.
[0052] Accordingly, the exhaust gas purification system for an
internal combustion engine according to the present invention may
be made to correct the degree of opening of the high pressure EGR
valve after the lapse of the predetermined period of time to an
open side (i.e., to a degree of opening larger than that in cases
where the above-mentioned supply processing has not been carried
out).
[0053] Because the path of the high pressure EGR gas is shorter
than the path of the low pressure EGR gas, the high pressure EGR
gas taken into the high pressure EGR passage from the exhaust
passage reaches the internal combustion engine earlier than the low
pressure EGR gas does. As a result, if the degree of opening of the
high pressure EGR valve after the elapse of the predetermined
period of time is corrected to the open side, it will become
possible to compensate for the amount of shortage or insufficiency
of the low pressure EGR gas with the high pressure EGR gas.
Effects of the Invention
[0054] According to the present invention, in an exhaust gas
purification system for an internal combustion engine which is
provided with a low pressure EGR device, it is possible to suppress
chemical changes in component parts arranged in a path of an EGR
gas, while suppressing an increase in the number of component
parts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] FIG. 1 is a view showing the schematic construction of an
exhaust gas purification system for an internal combustion engine
in a first embodiment of the present invention.
[0056] FIG. 2 is a flow chart showing an acid neutralization
processing routine in the first embodiment of the present
invention.
[0057] FIG. 3 is a view showing the schematic construction of an
exhaust gas purification system for an internal combustion engine
in a second embodiment of the present invention.
[0058] FIG. 4 is a flow chart showing an acid neutralization
processing routine in a third embodiment of the present
invention.
[0059] FIG. 5 is a view showing another construction example of an
exhaust gas purification system for an internal combustion engine
in the third embodiment of the present invention.
[0060] FIG. 6 is a view showing the schematic construction of an
exhaust gas purification system for an internal combustion engine
in a fourth embodiment of the present invention.
[0061] FIG. 7 is a flow chart showing an acid neutralization
processing routine in the fourth embodiment of the present
invention.
[0062] FIG. 8 is a view showing the relation between an amount of
saturation of ammonia and a bed temperature of a selective
reduction type catalyst.
[0063] FIG. 9 is a flow chart showing an acid neutralization
processing routine in a fifth embodiment of the present
invention.
[0064] FIG. 10 is a view showing the schematic construction of an
exhaust gas purification system for an internal combustion engine
in a sixth embodiment of the present invention.
[0065] FIG. 11 is a view showing the change of a bed temperature of
a selective reduction type catalyst and the change of an amount of
adsorption of ammonia thereof when acid neutralization processing
has been carried out in the sixth embodiment of the present
invention.
[0066] FIG. 12 is a flow chart showing an acid neutralization
processing routine in a sixth embodiment of the present
invention.
[0067] FIG. 13 is a flow chart showing an acid neutralization
processing routine in a seventh embodiment of the present
invention.
[0068] FIG. 14 is a flow chart showing an acid neutralization
processing routine in an eighth embodiment of the present
invention.
[0069] FIG. 15 is a flow chart showing a subroutine which is
executed by an ECU during or before acid neutralization processing
is carried out in the ninth embodiment of the present
invention.
[0070] FIG. 16 is a first view showing another example of the
subroutine in the ninth embodiment of the present invention.
[0071] FIG. 17 is a second view showing another example of the
subroutine in the ninth embodiment of the present invention.
THE MODE FOR CARRYING OUT THE INVENTION
[0072] Hereinafter, specific embodiments of the present invention
will be described based on the attached drawings. However, the
dimensions, materials, shapes, relative arrangements and so on of
component parts described in the embodiments are not intended to
limit the technical scope of the present invention to these alone
in particular as long as there are no specific statements.
First Embodiment
[0073] In the first place, a first embodiment of the present
invention will be described with reference to FIGS. 1 and 2. FIG. 1
is a view showing the schematic construction of an exhaust gas
purification system for an internal combustion engine in this first
embodiment.
[0074] An internal combustion engine 1 shown in FIG. 1 is a
compression ignition type internal combustion engine (diesel
engine) having four cylinders 2 for use in driving a vehicle. On
each of the cylinders 2 of the internal combustion engine 1, there
is mounted a fuel injection valve 3 for directly injecting fuel
into a corresponding cylinder 2.
[0075] An intake manifold 5 and an exhaust manifold 7 are connected
to the internal combustion engine 1. An intake passage 4 is
connected to the intake manifold 5. An exhaust passage 6 is
connected to the exhaust manifold 7. A centrifugal supercharger
(turbocharger) 8 has a compressor 8a arranged in the intake passage
4. The turbocharger 8 has a turbine 8b arranged in the exhaust
passage 6.
[0076] A first throttle valve 9 is arranged in the intake passage 4
at the downstream side of the compressor 8a. A second throttle
valve 19 is arranged in the intake passage 4 at the upstream side
of the compressor 8a. An intercooler 40 is arranged in the intake
passage 4 at the downstream side of the compressor 8a and at the
upstream side of the first throttle valve 9.
[0077] On the exhaust passage 6 at the downstream side of the
turbine 8b, there are arranged an oxidation catalyst 23, a
particulate filter 24, a selective reduction type catalyst 26, and
an exhaust throttle valve 27 in a sequential manner from an
upstream side along the direction of flow of the exhaust gas. The
selective reduction type catalyst 26 is a catalyst which serves to
adsorb polar molecules such as ammonia (NH.sub.3), in a selective
manner, and reduces and purifies nitrogen oxides (NOx) in the
exhaust gas by the use of the ammonia (NH.sub.3) thus adsorbed as a
reducing agent.
[0078] An addition valve 25 for supplying the reducing agent to the
above-mentioned selective reduction type catalyst 26 is mounted on
the exhaust passage 6 at a location between the particulate filter
24 and the selective reduction type catalyst 26. As the reducing
agent supplied from the addition valve 25, there can be exemplified
an ammonia derived compound in the form of a liquid, a gas, or a
solid. In this embodiment, it is assumed that an urea aqueous
solution is used as the reducing agent supplied from the addition
valve 25. Here, note that the addition valve 25 is merely one form
of the supply device according to the present invention.
[0079] The above-mentioned addition valve 25 serves to add the urea
aqueous solution into the exhaust passage 6 when the selective
reduction type catalyst 26 is in an active state. The urea aqueous
solution added into the exhaust passage 6 is thermally decomposed
and hydrolyzed in the exhaust gas or in the selective reduction
type catalyst 26 to generate ammonia (NH.sub.3). The ammonia
(NH.sub.3) generated in this manner is adsorbed to the selective
reduction type catalyst 26, thereby causing the nitrogen oxides
(Nox) in the exhaust gas to be reduced. Here, note that the
addition of the urea aqueous solution by means of the addition
valve 25 is to be carried out in a period or cycle which has been
set beforehand.
[0080] A high pressure EGR device 11 and a low pressure EGR device
15 are arranged in an intake and exhaust system of the internal
combustion engine 1. The high pressure EGR device 11 is provided
with a high pressure EGR passage 12, a high pressure EGR valve 13,
and a high pressure EGR cooler 14. The high pressure EGR passage 12
is connected at one end thereof to the exhaust manifold 7, and is
also connected at the other end thereof to a portion of the intake
passage 4 at the downstream side of the first throttle valve 9.
[0081] The high pressure EGR valve 13 and the high pressure EGR
cooler 14 are arranged in the high pressure EGR passage 12. The
flow rate of a high pressure EGR gas, which is introduced into the
intake passage 4 from the exhaust manifold 7 by way of the high
pressure EGR passage 12, is controlled by means of the high
pressure EGR valve 13.
[0082] The low pressure EGR device 15 is provided with a low
pressure EGR passage 16, a low pressure EGR valve 17, and a low
pressure EGR cooler 18. The low pressure EGR passage 16 is
connected at one end thereof to a portion of the exhaust passage 6
at the downstream side of the addition valve 25 and at the upstream
side of the selective reduction type catalyst 26, and is also
connected at the other end thereof to a portion of the intake
passage 4 at the downstream side of the second throttle valve 19
and at the upstream side of the compressor 8a.
[0083] The low pressure EGR valve 17 and the low pressure EGR
cooler 18 are arranged in the low pressure EGR passage 16. The flow
rate of a low pressure EGR gas, which is introduced into the intake
passage 4 from the exhaust passage 6 by way of the low pressure EGR
passage 16, is controlled by means of the low pressure EGR valve
17.
[0084] An electronic control unit (ECU) 20 is provided in
combination with the internal combustion engine 1 as constructed in
the above-mentioned manner. A variety of kinds of sensors, such as
a crank position sensor 21, an accelerator position sensor 22, an
exhaust gas temperature sensor 28 and so on, are electrically
connected to the ECU 20. The crank position sensor 21 is a sensor
which serves to detect the rotational position of an output shaft
(crankshaft) of the internal combustion engine 1. The accelerator
position sensor 22 is a sensor which serves to detect an amount of
operation (accelerator opening degree) of an accelerator pedal. The
exhaust gas temperature sensor 28 is a sensor which detects the
temperature of the exhaust gas flowing through the exhaust passage
6. Here, note that in the example shown in FIG. 1, the exhaust gas
temperature sensor 28 is arranged in the exhaust passage 6 at a
location between the particulate filter 24 and the addition valve
25, but it may be arranged in the exhaust passage 6 at a location
upstream of the oxidation catalyst 23, or on the exhaust passage 6
at a location downstream of the addition valve 25, or on the
exhaust passage 6 at a location downstream of the selective
reduction type catalyst 26.
[0085] In addition, a variety of kinds of equipment, such as the
fuel injection valve 3, the first throttle valve 9, the second
throttle valve 19, the addition valve 25, the high pressure EGR
valve 13, the low pressure EGR valve 17, the exhaust throttle valve
27 and so on, are electrically connected to the ECU 20. The ECU 20
controls the above-mentioned variety of kinds of equipment based on
the detection signals of the above-mentioned variety of kinds of
sensors.
[0086] For example, by causing the addition valve 25 to open in a
periodic manner when the internal combustion engine 1 is in an
operating state, the ECU 20 carries out processing to supply the
urea aqueous solution as the reducing agent to the selective
reduction type catalyst 26 (hereinafter referred to as "reducing
agent addition processing"). Moreover, by causing the addition
valve 25 to open when the low pressure EGR valve 17 is in a valve
open state, the ECU 20 carries out processing to neutralize acidic
substances which exists in the path of the low pressure EGR gas
(hereinafter referred to as "acid neutralization processing").
[0087] In the following, a method of carrying out the acid
neutralizing processing in this embodiment will be described.
[0088] Condensed water may accumulate in the path of the low
pressure EGR gas. When the condensed water comes in contact with
the low pressure EGR gas, the hydrogen ion exponent (power of
hydrogen: pH) of the condensed water may drop (be strongly
acidized). When condensed water with a low hydrogen ion exponent
(pH) and/or vaporized substances (acidic substances) of condensed
water flow into the compressor 8a, the intercooler 40 or the like
together with the low pressure EGR gas, a chemical change may be
made in the compressor 8a, the intercooler 40 or the like.
[0089] On the other hand, when the addition valve 25 is opened
during the time the low pressure EGR valve 17 in its valve open
state, a part of the urea aqueous solution added into the exhaust
gas from the addition valve 25 will flow into the low pressure EGR
passage 16. Here, note that the urea aqueous solution, when exposed
to the hot exhaust gas, is thermally decomposed and hydrolyzed to
generate ammonia (NH.sub.3). The ammonia (NH.sub.3) functions as a
neutralizing agent for the acidic substances. Therefore, as the
ammonia (NH.sub.3) flows through the path of the low pressure EGR
gas (the intake passage 4, the compressor 8a and the intercooler
40), the acidic substances existing in the path of the low pressure
EGR gas are neutralized by the ammonia (NH.sub.3). As a result, the
chemical change of the compressor 8a, the intercooler 40, or the
like can be suppressed.
[0090] Further, in the exhaust gas purification system for an
internal combustion engine of this embodiment, the selective
reduction type catalyst 26 is arranged in a portion of the exhaust
passage 6 at a location downstream of a connection portion of the
low pressure EGR passage 16, and hence, the pressure of the exhaust
gas at an upstream end of the low pressure EGR passage 16 (i.e., at
a connection position at which the low pressure EGR passage 16 and
the exhaust passage 6 are connected with each other) becomes high.
As the exhaust gas pressure at the upstream end of the low pressure
EGR passage 16 becomes high, it becomes easy for the exhaust gas to
flow from the exhaust passage 6 into the low pressure EGR passage
16. Therefore, it becomes unnecessary to throttle or decrease the
degree of opening of the exhaust throttle valve 27 to a large
extent at the time when the low pressure EGR valve 17 is opened. As
a result, it becomes possible to suppress a rise in back pressure
to a minimum level at the time of opening the low pressure EGR
valve 17.
[0091] Next, an execution procedure of the acid neutralization
processing in this embodiment will be described refer to FIG. 2.
FIG. 2 is a flow chart showing a control routine which the ECU 20
carries out at the time of executing the acid neutralization
processing. This control routine has been beforehand stored in a
ROM of the ECU 20, etc., and is carried out by the ECU 20 in a
periodical manner.
[0092] In the control routine of FIG. 2, the ECU 20 first carries
out the processing of step S101. That is, in step S101, the ECU 20
determines whether the low pressure EGR valve 17 is in its valve
open state. In cases where a negative determination is made in step
S101, the process of the ECU 20 goes to step S103. In step S103,
the ECU 20 controls the addition valve 25 in an ordinary manner.
That is, the ECU 20 supplies the urea aqueous solution to the
selective reduction type catalyst 26 by causing the addition valve
25 to open at a predetermined interval of time which has been set
beforehand.
[0093] On the other hand, in cases where an affirmative
determination is made in the above-mentioned step S101, the process
of the ECU 20 goes to step S102. In step S102, the ECU 20 causes
the addition valve 25 to open. By carrying out the processing of
step S102 in this manner by means of the ECU 20, a control unit
according to the present invention is achieved.
[0094] In cases where the above-mentioned processing of step S102
is carried out, a part of the urea aqueous solution added into the
exhaust gas from the addition valve 25 flows into the low pressure
EGR passage 16 while being thermally decomposed and hydrolyzed, and
the remaining urea aqueous solution is supplied to the selective
reduction type catalyst 26 while being thermally decomposed and
hydrolyzed.
[0095] The ammonia (NH.sub.3), which has flowed into the low
pressure EGR passage 16, serves to neutralize the acidic substances
existing in the path of the low pressure EGR gas. As a result, it
becomes possible to avoid a situation in which the compressor 8a
and the intercooler 40, which are arranged in the path of the low
pressure EGR gas, come into contact with the acidic substances
thereby to cause a chemical change.
[0096] According to the embodiment as described above, it is
possible to suppress chemical changes of the equipment and the
component parts which are arranged in the path of the low pressure
EGR gas. Moreover, because the addition valve 25 for supplying the
reducing agent to the selective reduction type catalyst 26 can be
used as the supply device for supplying the neutralizing agent to
the path of the low pressure EGR gas, it is not necessary to add
any new component parts.
[0097] Accordingly, it becomes possible to suppress chemical
changes in the component parts which are arranged in the path of
the low pressure EGR gas, while suppressing an increase in the
number of component parts.
[0098] Here, note that in this embodiment, there has been described
an example in which the acid neutralization processing is carried
out aside from the reducing agent addition processing, the reducing
agent addition processing may be used as the acid neutralization
processing as well by permitting the execution of the reducing
agent addition processing at the time when the low pressure EGR
valve 17 is in a valve open state. According to such a method, it
becomes unnecessary to carry out the acid neutralization processing
separately from the reducing agent addition processing, thus making
it possible to attain the simplification of a control logic.
[0099] However, when the reducing agent addition processing is
carried out during the time the low pressure EGR valve 17 in its
valve open state, a part of the reducing agent flows into the low
pressure EGR passage 16, so the reducing agent supplied to the
selective reduction type catalyst 26 may become short or
insufficient. Accordingly, in cases where the reducing agent
addition processing is carried out at the time when the low
pressure EGR valve 17 is in its valve open state, the amount of
addition of the reducing agent may be caused to increase in
comparison with the case where the reducing agent addition
processing is carried out at the time when the low pressure EGR
valve 17 is in its valve closed state.
[0100] In addition, in this embodiment, there has been described an
example in which the acid neutralization processing is carried out
on the condition that the low pressure EGR valve 17 is in its valve
open state, but the acid neutralization processing may be carried
out on the condition that the temperature of the low pressure EGR
gas is not less than a reference temperature, in addition to the
condition that the low pressure EGR valve 17 is in its valve open
state. The reference temperature referred to herein is a
temperature which is equal to a lower limit value of a temperature
range in which the urea aqueous solution is thermally decomposed
and hydrolyzed, or which is a little higher than the lower limit
value of the above-mentioned temperature range.
[0101] When the acid neutralization processing is carried out
according to such conditions, a substance (ammonia (NH.sub.3)) with
a high capacity as a neutralizing agent can be supplied to the path
of the low pressure EGR gas. As a result, it becomes possible to
neutralize the acidic substances existing in the path of the low
pressure EGR gas in a more reliable manner. Here, note that as the
temperature of the low pressure EGR gas, there can be used the
detected signal value of the exhaust gas temperature sensor 28.
[0102] Although in this embodiment, reference has been made to an
example in which the acid neutralization processing is carried out
in a periodic manner, such processing may be carried out by being
triggered when the hydrogen ion exponent (pH) of a substance which
exists in the path of the low pressure EGR gas has become not more
than a predetermined value. The above-mentioned predetermined value
is a value which is determined based on a maximum value of the
hydrogen ion exponent (pH) considered to cause a chemical change of
a component part such as the compressor 8a, the intercooler 40 or
the like, and is set to be, for example, a value which is a little
larger than the above-mentioned maximum value.
[0103] As a method of obtaining the hydrogen ion exponent (pH) of
the substance existing in the path of the low pressure EGR gas,
there can be exemplified a method of arranging a pH sensor at a
location in the path of the low pressure EGR gas at which condensed
water is apt to accumulate, a method of obtaining the hydrogen ion
exponent (pH) of the substance from a map or a computational model
using, as an argument, an operational history of the internal
combustion engine 1 (e.g., an integrated value of the number of
engine revolutions per unit time, an integrated value of an amount
of fuel injection, an integrated value of an amount of low pressure
EGR gas, etc.), a method of obtaining the hydrogen ion exponent
(pH) of the substance from a map or a computational model using, as
arguments, an integrated amount of the nitrogen oxides (NOx) which
have flowed into the path of the low pressure EGR gas, and a
temperature in the path of the low pressure EGR gas, and so on.
[0104] On the other hand, the acid neutralization processing may be
carried out by being triggered when the amount of the acidic
substances existing in the path of the low pressure EGR gas has
exceeded a threshold value which has been set beforehand. As a
method of obtaining the amount of the acidic substances existing in
the path of the low pressure EGR gas, there can be exemplified a
method of obtaining it from a map or a computational model using,
as an argument, an operational history of the internal combustion
engine 1 (e.g., an integrated value of the number of engine
revolutions per unit time, an integrated value of an amount of fuel
injection, an integrated value of the low pressure EGR gas, etc.),
and a method of obtaining it from a map or a computational model
using, as an argument, an integrated amount of the nitrogen oxides
(NOx) which has flowed into the low pressure EGR gas passage 16, a
temperature in the path of the low pressure EGR gas, or the
like.
Second Embodiment
[0105] Next, a second embodiment of the present invention will be
described with reference to FIG. 3. Here, a construction different
from that of the above-mentioned first embodiment will be
described, and an explanation of the same construction will be
omitted.
[0106] The difference of this second embodiment from the
above-mentioned first embodiment is that a dispersion plate for
dispersing an urea aqueous solution supplied from the addition
valve 25 is arranged in a portion of the exhaust passage 6 at the
upstream side of the selective reduction type catalyst 26.
[0107] FIG. 3 is a view showing the schematic construction of an
exhaust gas purification system for an internal combustion engine
in this second embodiment. As shown in FIG. 3, the dispersion plate
29 is arranged in a portion of the exhaust passage 6 at the
upstream side of the selective reduction type catalyst 26 and at
the downstream side of the connection portion of the low pressure
EGR passage 16. The other construction of this second embodiment is
the same as that of the above-mentioned first embodiment.
[0108] In cases where the dispersion plate 29 is arranged in that
portion of the exhaust passage 6 which is at the upstream side of
the selective reduction type catalyst 26 and at the downstream side
of the connection portion of the low pressure EGR passage 16, it is
possible to make the pressure in the low pressure EGR passage 16 at
an upstream end thereof higher in comparison with the case where
the dispersion plate 29 is not arranged, or the case where the
dispersion plate 29 is arranged in a portion of the exhaust passage
6 at the upstream side of the connection portion of the low
pressure EGR passage 16.
[0109] Therefore, it becomes easy for the exhaust gas (the low
pressure EGR gas) to flow into the low pressure EGR passage 16 from
the exhaust passage 6 at the time when the low pressure EGR valve
17 is opened. As a result, it is possible to make larger the degree
of opening of the exhaust throttle valve 27 at the time when the
low pressure EGR valve 17.
Third Embodiment
[0110] Now, a third embodiment of the present invention will be
described with reference to FIGS. 4 and 5. Here, a construction
different from that of the above-mentioned first embodiment will be
described, and an explanation of the same construction will be
omitted.
[0111] The difference of this third embodiment from the
above-mentioned first embodiment is that acid neutralization
processing is carried out during the time when deceleration fuel
cut-off control of the internal combustion engine 1 is in an
execution state.
[0112] In the following, an execution procedure of the acid
neutralization processing in this embodiment will be described
refer to FIG. 4. FIG. 4 is a flow chart showing a control routine
which the ECU 20 carries out at the time of executing the acid
neutralization processing. This control routine has been beforehand
stored in the ROM of the ECU 20, etc., and is carried out by the
ECU 20 in a periodical manner.
[0113] In the control routine of FIG. 4, the ECU 20 determines in
step S201 whether the deceleration fuel cut-off control of the
internal combustion engine 1 is being carried out. In cases where a
negative determination is made in step S201, the ECU 20 once exits
this routine. On the other hand, in cases where an affirmative
determination is made in step S201, the process of the ECU 20 goes
to step S202.
[0114] In step S202, the ECU 20 reads in a detected value of the
exhaust gas temperature sensor 28 (a temperature of the exhaust
gas). By carrying out the processing of step S202 in this manner by
means of the ECU 20, a detection unit according to the present
invention is achieved.
[0115] Subsequently, the process of the ECU 20 goes to step S203,
in which it is determined whether the temperature of the exhaust
gas thus read in the above-mentioned step S202 is not less than a
reference temperature. The reference temperature referred to herein
is a temperature which is equal to a lower limit value of a
temperature range in which the urea aqueous solution can be
thermally decomposed and hydrolyzed, or which is a little higher
than the lower limit value of the above-mentioned temperature
range.
[0116] In cases where a negative determination is made in the
above-mentioned step S203 (the exhaust gas temperature<the
reference temperature), the ECU 20 once terminates the execution of
this routine. On the other hand, in cases where a affirmative
determination is made in the above-mentioned step S203 (the exhaust
gas temperature the reference temperature), the process of the ECU
20 goes to step S204.
[0117] In step S204, the ECU 20 causes the second throttle valve 19
and the exhaust throttle valve 27 to close. Subsequently, the
process of the ECU 20 goes to step S205, in which a predetermined
amount of urea aqueous solution is added from the addition valve
25. The above-mentioned predetermined amount is a fixed amount
which has been beforehand determined, and is a value which has been
beforehand set by adaptation or calibration processing making use
of experiments, etc.
[0118] In step S206, the ECU 20 determines whether a termination
condition for the deceleration fuel cut-off control has been
satisfied. As the termination condition for the deceleration fuel
cut-off control, there can be exemplified a condition in which the
number of engine revolutions per unit time is not more than a
predetermined lower limit value, or a condition in which a detected
signal of the accelerator position sensor 22 (the degree of opening
of the accelerator pedal) is larger than zero, or the like.
[0119] In cases where a negative determination is made in the
above-mentioned step S206, the ECU 20 continues to carry out the
processing of step S206 until the termination condition for the
deceleration fuel cut-off control is satisfied. On the other hand,
in cases where an affirmative determination is made in the
above-mentioned step S206, the process of the ECU 20 goes to step
S207.
[0120] In step S207, the ECU 20 returns the degree of opening of
the second throttle valve 19 and the degree of opening of the
exhaust throttle valve 27 to their ordinary degrees of opening,
respectively.
[0121] According to the embodiment as described above, all of the
urea aqueous solution supplied from the addition valve 25 will flow
into the path of the low pressure EGR gas, so it becomes easy to
regulate the amount of the urea aqueous solution to be supplied to
the path of the low pressure EGR gas. Moreover, even if acid
neutralization processing is carried out when the selective
reduction type catalyst 26 is in a state where ammonia (NH.sub.3)
can not be adsorbed thereto, it is possible to avoid the situation
where ammonia (NH.sub.3) is released into the atmospheric air.
[0122] Here, note that when the deceleration fuel cut-off control
of the internal combustion engine 1 is carried out, the temperature
of the exhaust gas becomes lower in comparison with the time in
which fuel is burned in the internal combustion engine 1. For that
reason, there will be a possibility that opportunities for the
temperature of the exhaust gas to become not less than the
reference temperature, in other words, opportunities to carry out
acid neutralization processing, may decrease.
[0123] Accordingly, a catalyst 30 for hydrolysis may be arranged in
a portion of the exhaust passage 6 at the downstream side of the
addition valve 25 and at the upstream side of the connection
portion of the low pressure EGR passage 16, as shown in FIG. 5. In
that case, even in cases where the temperature of the exhaust gas
is lower than the reference temperature, it becomes possible to
carry out acid neutralization processing as long as the hydrolysis
catalyst 30 is in an active state.
[0124] The hydrolysis catalyst may instead be arranged in the low
pressure EGR passage 16. However, when the hydrolysis catalyst is
arranged in the low pressure EGR passage 16, it may become
difficult for the exhaust gas to flow from the exhaust passage 6
into the low pressure EGR passage 16 due to pressure loss of the
catalyst. In such a case, it becomes necessary to make small the
degree of opening of the exhaust throttle valve 27, so the back
pressure of the internal combustion engine 1 will rise. For this
reason, it is desirable that the hydrolysis catalyst be arranged in
that portion of the exhaust passage 6 which is at the downstream
side of the addition valve 25 and at the upstream side of the
connection portion of the low pressure EGR passage 16, as shown in
FIG. 5 referred to above.
[0125] In addition, a heating device for heating the exhaust gas
may be arranged instead of the above-mentioned hydrolysis catalyst.
As the heating device, there can be exemplified an electric heater
that serves to convert electrical energy into thermal or heat
energy.
[0126] However, in cases where the acid neutralization processing
is carried as referred to above, the amount of oxygen introduced
into combustion chambers of the internal combustion engine 1 after
the deceleration fuel cut-off control has been terminated may
become excessively small. Moreover, carbon dioxide (CO.sub.2) and
water (H.sub.2O), which have been produced by the hydrolysis of the
urea aqueous solution will also be introduced into the combustion
chambers. As a result, it is considered that the combustion
stability of the internal combustion engine 1 falls or a misfire
occurs, immediately after the termination of the deceleration fuel
cut-off control.
[0127] Accordingly, in cases where the acid neutralization
processing is carried out during the execution of the deceleration
fuel cut-off control, the ECU 20 may carry out processing to make
the degree of opening of the low pressure EGR valve 17 in a
predetermined period of time after the termination of the
deceleration fuel cut-off control smaller than a target degree of
opening (i.e., a target degree of opening which is decided
according to the operational condition of the internal combustion
engine 1), or may carry out processing to cause the low pressure
EGR valve 17 to close (hereinafter referred to as "scavenging
processing").
[0128] The above-mentioned predetermined period of time is a period
of time taken until the gas existing in a portion of the intake
passage 4 at the downstream side of the connection portion of the
low pressure EGR passage 16 has been scavenged. The predetermined
period of time can be calculated by using, as parameters, the
volume of a path extending from the connection portion of the low
pressure EGR passage 16 to the combustion chambers of the internal
combustion engine 1, and the number of engine revolutions per unit
time (the amount of gas which is taken in per unit time by the
internal combustion engine 1).
[0129] When the scavenging processing as stated above is carried
out, it is possible to avoid the situation where after the
termination of the deceleration fuel cut-off control, the amount of
oxygen introduced into each of the combustion chambers of the
internal combustion engine 1 becomes short, or the amount of carbon
dioxide (CO.sub.2) or water (H.sub.2O) becomes excessive. As a
result, it is also possible to avoid the situation where the
combustion stability of the internal combustion engine 1 becomes
low or a misfire occurs, after the termination of the deceleration
fuel cut-off control.
[0130] Here, note that after the termination of the above-mentioned
scavenging processing, it is necessary to increase the amount of
low pressure EGR gas introduced into the combustion chambers of the
internal combustion engine 1 to a target amount (i.e., a target
amount of low pressure EGR gas in the case where the acid
neutralization processing and the scavenging processing are not
carried out). However, some time will be taken before the low
pressure EGR gas arrives at each of the combustion chambers of the
internal combustion engine 1, and hence, the amount of low pressure
EGR gas introduced into each of the combustion chambers of the
internal combustion engine 1 after the termination of the
scavenging processing may be short or insufficient. If the low
pressure EGR gas runs short, there can be a situation where the
amount of production of nitrogen oxides (NOx) increases, or a
situation where combustion noise becomes large.
[0131] To cope with such situations, the ECU 20 may correct or
adjust the degree of opening of the high pressure EGR valve 13
after the termination of the scavenging processing in a more open
(increasing) direction from a degree of opening thereof in the case
where the scavenging processing is not carried out. An amount of
correction or adjustment in that case may be a fixed value, or may
be a variable value which is changed according to an amount of
shortage of the low pressure EGR gas.
[0132] In addition, in this embodiment, reference has been made to
an example in which acid neutralization processing is carried out
on the condition that deceleration fuel cut-off control is being
executed, but acid neutralization processing may instead be carried
out on the condition that deceleration fuel cut-off control is
being executed, and the hydrogen ion exponent (pH) of a substance
existing in the path of the low pressure EGR gas is not more than
the predetermined value. In that case, it is possible to suppress
the amount of the urea aqueous solution supplied from the addition
valve 25 to a necessity minimum.
Fourth Embodiment
[0133] Next, a fourth embodiment of the present invention will be
described with reference to FIGS. 6 through 8. Here, a construction
different from that of the above-mentioned first embodiment will be
described, and an explanation of the same construction will be
omitted.
[0134] The difference of this fourth embodiment from the
above-mentioned first embodiment is that the selective reduction
type catalyst 26 is arranged in a portion of the exhaust passage 6
at the upstream side of the connection portion of the low pressure
EGR passage 16.
[0135] FIG. 6 is a view showing the schematic construction of an
exhaust gas purification system for an internal combustion engine
in this fourth embodiment. In FIG. 6, the selective reduction type
catalyst 26 is arranged in that portion of the exhaust passage 6
which is at the upstream side of the connection portion of the low
pressure EGR passage 16 and at the downstream side of the addition
valve 25.
[0136] When acid neutralization processing is carried out in the
construction in which the selective reduction type catalyst 26 is
arranged in the portion of the exhaust passage 6 at the upstream
side of the connection portion of the low pressure EGR passage 16,
the ammonia (NH.sub.3) supplied from the addition valve 25 will be
adsorbed to the selective reduction type catalyst 26.
[0137] However, the amount of ammonia (NH.sub.3) which can be
adsorbed by the selective reduction type catalyst 26 is limited.
Accordingly, in the acid neutralization processing in this
embodiment, the ECU 20 serves to control the addition valve 25 in
such a manner that an amount of ammonia (NH.sub.3), which is more
than an amount of ammonia (NH.sub.3) which can be adsorbed by the
selective reduction type catalyst 26 (hereinafter referred to as an
"amount of saturation of ammonia"), is supplied to the selective
reduction type catalyst 26.
[0138] In the following, an execution procedure of the acid
neutralization processing in this embodiment will be described
refer to FIG. 7. FIG. 7 is a flow chart showing a control routine
which the ECU 20 carries out at the time of executing the acid
neutralization processing. This control routine has been beforehand
stored in the ROM of the ECU 20, etc., and is carried out by the
ECU 20 in a periodical manner.
[0139] In the control routine of FIG. 7, first in step S301, the
ECU 20 determines whether an execution condition for the acid
neutralization processing is satisfied. The acid neutralization
processing execution condition is satisfied, for example, when an
amount (i.e., an amount of ions or a molar quantity) Gac of the
acidic substances existing in the path of the low pressure EGR gas
exceeds a threshold value, and when the low pressure EGR valve 17
is in a valve open state.
[0140] Here, note that as a method of obtaining the amount Gac of
the acidic substances existing in the path of the low pressure EGR
gas, there can be exemplified a method of obtaining it from a map
or a computational model using, as an argument, an operational
history of the internal combustion engine 1 (e.g., an integrated
value of the number of engine revolutions per unit time, an
integrated value of an amount of fuel injection, an integrated
value of the low pressure EGR gas, etc.), or a method of obtaining
it from a map or a computational model using, as an argument, an
integrated amount of the nitrogen oxides (NOx) which has flowed
into the low pressure EGR gas passage 16, a temperature in the path
of the low pressure EGR gas, or the like. By obtaining the amount
Gac of the acidic substances according to such a method by means of
the ECU 20, an obtaining unit according to the present invention is
achieved.
[0141] In cases where a negative determination is made in the
above-mentioned step S301, the ECU 20 once terminates the execution
of this routine. On the other hand, in cases where an affirmative
determination is made in the above-mentioned step S301, the process
of the ECU 20 goes to step S302.
[0142] In S302, the ECU 20 starts to supply an urea aqueous
solution by causing the addition valve 25 to open. In that case,
the ECU 20 regulates the amount of the urea aqueous solution to be
supplied in such a manner that an amount of ammonia (NH.sub.3) more
than the amount of saturation of ammonia of the selective reduction
type catalyst 26 is supplied to the selective reduction type
catalyst 26.
[0143] FIG. 8 is a view showing the relation between the amount of
saturation of ammonia in the selective reduction type catalyst 26
and the bed temperature of the selective reduction type catalyst
26. As shown in FIG. 8, the amount of saturation of ammonia in the
selective reduction type catalyst 26 changes according to the bed
temperature of the selective reduction type catalyst 26. For
example, when the bed temperature of the selective reduction type
catalyst 26 is low, the amount of saturation of ammonia becomes
larger than when the bed temperature of the selective reduction
type catalyst 26 is high. Accordingly, the ECU 20 calculates the
amount of saturation of ammonia by using the bed temperature of the
selective reduction type catalyst 26 as a parameter, and controls
the addition valve 25 in such a manner that an amount of ammonia
(NH.sub.3) more than the amount of saturation of ammonia is
supplied to the selective reduction type catalyst 26.
[0144] When an amount of ammonia (NH.sub.3) more than the amount of
saturation of ammonia is supplied to the selective reduction type
catalyst 26 in this manner, an excessive or surplus amount of
ammonia (NH.sub.3), which has not been adsorbed by the selective
reduction type catalyst 26, will flow to the downstream of the
selective reduction type catalyst 26. A part of ammonia (NH.sub.3)
having flowed to the downstream of the selective reduction type
catalyst 26 flows into the low pressure EGR passage 16 together
with the low pressure EGR gas. The ammonia (NH.sub.3), which has
flowed into the low pressure EGR passage 16, acts as a neutralizing
agent for the acidic substances existing in the path of the low
pressure EGR gas.
[0145] Here, returning to the control routine of FIG. 7, the ECU 20
calculates, in step S303, a total amount Gnh31pl of the ammonia
(NH.sub.3) which has flowed into the low pressure EGR passage 16.
Specifically, the ECU 20 first obtains the amount of the ammonia
(NH.sub.3) which flows out of the selective reduction type catalyst
26. That is, the ECU 20 calculates a concentration Cnh3rl of the
ammonia (NH.sub.3) contained in the exhaust gas which flows out of
the selective reduction type catalyst 26. The concentration Cnh3rl
of the ammonia (NH.sub.3) contained in the exhaust gas may be
obtained by means of a map or a computational model which uses, as
arguments, the bed temperature of the selective reduction type
catalyst 26 and the flow speed of the exhaust gas, or it may be
obtained by means of a map or a computational model which uses, as
arguments, the flow rate of the exhaust gas and the detected value
of an ammonia sensor.
[0146] Subsequently, the ECU 20 obtains the amount of the exhaust
gas flowing from the exhaust passage 6 into the low pressure EGR
passage 16, i.e., the amount of low pressure EGR gas G1pl. The
amount of low pressure EGR gas G1pl can be obtained by means of a
map or a computational model which uses, as arguments, the
operational condition (the amount of intake air, the number of
engine revolutions per unit time, etc.) of the internal combustion
engine 1, the degree of opening of the low pressure EGR valve 17,
the degree of opening of the exhaust throttle valve 27, and so
on.
[0147] The ECU 20 calculates an amount (=Cnh3rl*G1pl) of the
ammonia (NH.sub.3) to be introduced into the low pressure EGR
passage 16 by multiplying the concentration Cnh3rl of ammonia
(NH.sub.3) and the amount of low pressure EGR gas G1pl together.
Moreover, the ECU 20 calculates the above-mentioned total amount
Gnh31pl (=.SIGMA.(Cnh3rl*G1pl)) by integrating the amount of the
ammonia (NH.sub.3) introduced into the low pressure EGR passage
16.
[0148] In step S304, the ECU 20 determines whether the total amount
Gnh31pl obtained in the above-mentioned step S303 is not less than
the amount Gac of acidic substances which was calculated in the
above-mentioned step S301. In cases where a negative determination
is made in step S304 (Gnh31pl<Gac), the ECU 20 returns to the
above-mentioned step S303. On the other hand, in cases where an
affirmative determination is made in step S304
(Gnh31pl.gtoreq.Gac), the process of the ECU 20 goes to step S305,
in which the addition valve 25 is caused to close.
[0149] Subsequently, in step S306, the ECU 20 resets the calculated
value of the amount Gac of the acidic substances existing in the
path of the low pressure EGR gas to zero, and terminates the
execution of this routine.
[0150] According to the embodiment described above, even in the
construction in which the selective reduction type catalyst 26 is
arranged at the upstream side of the connection portion of the low
pressure EGR passage 16, the acidic substances existing in the path
of the low pressure EGR gas can be neutralized. Moreover, according
to this embodiment, the amount of supply of the urea aqueous
solution is regulated according to the amount of the acidic
substances existing in the path of the low pressure EGR gas, and
hence, the amount of consumption of the urea aqueous solution
accompanying the execution of acid neutralization processing can be
suppressed to a necessity minimum.
[0151] Here, note that when acid neutralization processing is
carried out in the construction in which the selective reduction
type catalyst 26 is arranged in a portion of the exhaust passage 6
at the upstream side of the connection portion of the low pressure
EGR passage 16, a part of the ammonia (NH.sub.3) having flowed out
of the selective reduction type catalyst 26 flows into the low
pressure EGR passage 16, but the remaining ammonia (NH.sub.3) will
be discharged into the atmospheric air. Accordingly, a catalyst for
oxidizing ammonia (NH.sub.3) may be arranged in a portion of the
exhaust passage 6 at the downstream side of the connection portion
of the low pressure EGR passage 16.
Fifth Embodiment
[0152] Next, a fifth embodiment of the present invention will be
described with reference to FIG. 9. Here, a construction different
from that of the above-mentioned fourth embodiment will be
described, and an explanation of the same construction will be
omitted.
[0153] The difference of this fourth embodiment from the
above-mentioned fourth embodiment is that in cases where acid
neutralization processing is carried out during the execution of
deceleration fuel cut-off control, the exhaust throttle valve 27 is
caused to close.
[0154] In the following, an execution procedure of the acid
neutralization processing in this embodiment will be described
refer to FIG. 9. FIG. 9 is a flow chart showing a control routine
which is executed by the ECU 20 at the time when the acid
neutralization processing is carried out in this embodiment. Here,
note that in FIG. 9, the same symbols are attached to the same
processes as those in the above-mentioned control routine of the
fourth embodiment (see FIG. 7).
[0155] In the control routine of FIG. 9, the ECU 20 carries out the
processing of step S401 after having executed the processing of
S302. In step S401, the ECU 20 determines whether deceleration fuel
cut-off control is being carried out.
[0156] In cases where an affirmative determination is made in the
above-mentioned step S401, the process of the ECU 20 goes to step
S402, in which the second throttle valve 19 and the exhaust
throttle valve 27 are caused to close, and at the same time, the
low pressure EGR valve 17 is caused to open. When the acid
neutralization processing is carried out in such a state, all of
the ammonia (NH.sub.3) having flowed out of the selective reduction
type catalyst 26 will flow into the low pressure EGR passage 16. In
other words, all of the ammonia (NH.sub.3) having flowed out of the
selective reduction type catalyst 26 can be used as a neutralizing
agent. As a result, the acidic substances can be neutralized, while
suppressing the amount of consumption of the urea aqueous solution
accompanying the execution of the acid neutralization processing to
a small level.
[0157] In addition, in cases where a negative determination is made
in the above-mentioned step S401, the process of the ECU 20 goes to
step S403, in which the degrees of opening of the second throttle
valve 19, the exhaust throttle valve 27 and the low pressure EGR
valve 17 are controlled to their ordinary degrees of opening,
respectively.
[0158] Here, note that in this embodiment, reference has been made
to an example in which acid neutralization processing is carried
out even at the time of non-execution of deceleration fuel cut-off
control, but acid neutralization processing may be carried out only
at the time of execution of deceleration fuel cut-off control. In
that case, it is possible to suppress the amount of consumption of
the urea aqueous solution accompanying the execution of the acid
neutralization processing to a much smaller level.
Sixth Embodiment
[0159] Next, a sixth embodiment of the present invention will be
described with reference to FIGS. 10 through 12. Here, a
construction different from that of the above-mentioned fourth
embodiment will be described, and an explanation of the same
construction will be omitted.
[0160] The difference of this sixth embodiment from the
above-mentioned fourth embodiment is that provision is made for a
heating unit for heating the selective reduction type catalyst 26,
and that the heating unit is caused to operate during the execution
of acid neutralization processing.
[0161] FIG. 10 is a view showing the schematic construction of an
exhaust gas purification system for an internal combustion engine
in this sixth embodiment. In FIG. 10, a heater 260 for heating the
selective reduction type catalyst 26 is mounted on the selective
reduction type catalyst 26. The heater 260 is to convert the
electrical energy supplied from a battery into thermal or heat
energy thereby to heat the selective reduction type catalyst 26.
The other construction of this sixth embodiment is the same as that
of the above-mentioned fourth embodiment.
[0162] In cases where acid neutralization processing is carried out
in the exhaust gas purification system for an internal combustion
engine as constructed in this manner, the ECU 20 causes the urea
aqueous solution to be supplied from the addition valve 25, and at
the same time, operates the heater 260.
[0163] Specifically, when the execution condition for acid
neutralization processing is satisfied, the ECU 20 obtains the bed
temperature of the selective reduction type catalyst 26, and
decides a target value for the amount of adsorption of ammonia (a
target amount of supply thereof) based on the bed temperature thus
obtained. The target amount of supply in that case is set to an
amount which is smaller than the amount of saturation of
ammonia.
[0164] Subsequently, the ECU 20 causes the addition valve 25 to
open in accordance with the target amount of supply, and at the
same time, operates the heater 260. When the bed temperature of the
selective reduction type catalyst 26 is high, the amount of
saturation of ammonia becomes smaller than when the bed temperature
of the selective reduction type catalyst 26 is low. For that
reason, as the selective reduction type catalyst 26 is heated by
means of the heater 260, the amount of saturation of ammonia will
come to be less than the target amount of supply. As a result, a
part of the ammonia (NH.sub.3) supplied to the selective reduction
type catalyst 26 will flow to the downstream of the selective
reduction type catalyst 26.
[0165] Here, the change of the bed temperature of the selective
reduction type catalyst 26 and the change of the amount of
adsorption of ammonia thereof when acid neutralization processing
has been carried out are shown in FIG. 11. A solid line in FIG. 11
indicates the amount of saturation of ammonia, and an alternate
long and short dashed line indicates the target value for the
amount of adsorption of ammonia (in other words, the target amount
of supply of ammonia (NH.sub.3)). In addition, a symbol tcat1 in
FIG. 11 indicates a bed temperature of the selective reduction type
catalyst 26 when the execution condition for acid neutralization
processing has been satisfied, and a symbol tcat2 indicates a bed
temperature when the selective reduction type catalyst 26 has been
heated by means of the heater 260. Moreover, a symbol anh0 in FIG.
11 indicates an amount of saturation of ammonia when the bed
temperature of the selective reduction type catalyst 26 is tcat1; a
symbol anh1 (<anh0) indicates the target amount of supply of
ammonia (NH.sub.3) in the acid neutralization processing; and a
symbol anh2 (<anh1) indicates an amount of saturation of ammonia
(an amount of adsorption of ammonia) when the bed temperature of
the selective reduction type catalyst 26 has risen to tcat2.
[0166] As shown in FIG. 11, when the bed temperature of the
selective reduction type catalyst 26 goes up from tcat1 to tcat2,
the amount of saturation of ammonia decreases from anh0 to anh2.
Because the amount of saturation of ammonia anh2 is less than the
target amount of supply anh1, a surplus amount (=anh1-anh2) of
ammonia (NH.sub.3) will flow to a portion of the exhaust passage 6
at the downstream side of the selective reduction type catalyst 26.
A part of the ammonia (NH.sub.3) having flowed to the portion of
the exhaust passage 6 at the downstream side of the selective
reduction type catalyst 26 flows into the low pressure EGR passage
16, and acts as a neutralizing agent for the acidic substances.
[0167] When the selective reduction type catalyst 26 is heated in
this manner at the time of the execution of the acid neutralization
processing, it becomes unnecessary to supply to the selective
reduction type catalyst 26 an amount of ammonia (NH.sub.3) which is
larger than the amount of saturation of ammonia (i.e., the amount
of saturation of ammonia corresponding to the bed temperature at
the time when the execution condition for acid neutralization
processing has been satisfied). As a result, it is possible to
suppress an increase in the amount of consumption of the urea
aqueous solution accompanying the execution of the acid
neutralization processing to a small level.
[0168] In addition, because the operation of the heater 260 is
stopped after the acid neutralization processing has been
completed, the bed temperature of the selective reduction type
catalyst 26 drops. As the bed temperature of the selective
reduction type catalyst 26 drops, the amount of saturation of
ammonia increases. As a result, a margin is generated for the
ammonia adsorption capacity of the selective reduction type
catalyst 26, thus making it possible to avoid the situation where
ammonia (NH.sub.3) flows out to the downstream side of the
selective reduction type catalyst 26.
[0169] In the following, an execution procedure of the acid
neutralization processing in this embodiment will be described
refer to a flow chart of FIG. 12. FIG. 12 is a flow chart showing a
control routine which is executed by the ECU 20 at the time when
the acid neutralization processing is carried out. In FIG. 12, the
same symbols are attached to the same processes as those in the
above-mentioned control routine of the fourth embodiment (see FIG.
7).
[0170] In the control routine of FIG. 12, the ECU 20 carries out
the processing of step S501 after having executed the processing of
S302. In step S501, the ECU 20 causes the heater 260 to operate.
Here, note that in step S302 of this routine, the ECU 20 is assumed
to control the addition valve 25 in such a manner that the amount
(the target amount of supply) anh1 of the ammonia (NH.sub.3)
supplied to the selective reduction type catalyst 26 becomes less
than the amount of saturation of ammonia anh0, as referred to in
the above-mentioned description of FIG. 11.
[0171] The ECU 20 carries out the processing of steps S303 through
S305 after the execution of the processing of step S501. Here, note
that in cases where the amount of the ammonia (NH.sub.3) flowing
out of the selective reduction type catalyst 26 is obtained in step
S303, the ECU 20 is assumed to use a bed temperature tcat at the
present point in time, the target amount of supply anh1, and a map
as shown in the above-mentioned FIG. 11. That is, the ECU 20
obtains the amount of saturation of ammonia anh corresponding to
the bed temperature tcat at the present point in time from the map
of FIG. 11. Subsequently, the ECU 20 calculates the amount of the
ammonia (NH.sub.3) flowing out of the selective reduction type
catalyst 26 by subtracting the amount of saturation of ammonia anh
from the target amount of supply anh1.
[0172] The ECU 20 carries out the processing of step S502 after the
execution of the processing of step S305. In step S502, the ECU 20
causes the heater 260 to stop. In that case, the bed temperature of
the selective reduction type catalyst 26 drops, so the amount of
saturation of ammonia increases. As a result, it is possible to
avoid the situation where ammonia (NH.sub.3) flows out of the
selective reduction type catalyst 26 after the termination of the
acid neutralization processing.
[0173] According to the embodiment described above, the acidic
substances in the path of the low pressure EGR gas can be
neutralized, while suppressing the amount of consumption of the
urea aqueous solution to a smaller level than in the
above-mentioned fourth embodiment.
[0174] Here, note that in cases where a negative determination is
made in step S304 of the above-mentioned control routine, the ECU
20 may increase the amount of the urea aqueous solution to be
supplied from the addition valve 25, as long as an amount of
adsorption of ammonia at that point in time is less than a
remaining amount of the acidic substances (=Gac-Gnh31pl). In that
case, it becomes possible to neutralize the acidic substances
existing in the path of the low pressure EGR gas in a more reliable
manner.
[0175] In addition, in this embodiment, the heater mounted on the
selective reduction type catalyst 26 has been exemplified as a
means for heating the selective reduction type catalyst 26, but a
heater may instead be arranged in such a manner as to heat the
exhaust gas flowing into the selective reduction type catalyst
26.
[0176] As other methods of achieving the heating unit, the
temperature of the exhaust gas flowing into the selective reduction
type catalyst 26 may be raised by carrying out at least one of the
following control operations by means of the ECU 20, i.e., a
control operation to correct or adjust the degree of opening of the
second throttle valve 19 to a closed side, a control operation to
cause the amount of the low pressure EGR gas or the high pressure
EGR gas to increase, a control operation to correct or adjust the
degree of opening of the exhaust throttle valve 27 to a closed
side, a control operation to retard the fuel injection timing of
the fuel injection valve 3 (i.e., a control operation to retard the
combustion timing of fuel), and a control operation to supply
unburnt fuel to the oxidation catalyst 23.
[0177] In cases where the internal combustion engine 1 is provided
with a mechanism capable of changing the valve opening timing of
each exhaust valve, the temperature of the exhaust gas flowing into
the selective reduction type catalyst 26 may be raised by advancing
the valve opening timing of each exhaust valve by means of the ECU
20.
[0178] In cases where the turbocharger 8 is a variable capacity
type turbo charger, the temperature of the exhaust gas flowing into
the selective reduction type catalyst 26 may be raised by
correcting the degree of opening of a nozzle vane of the variable
capacity type turbo charger to an open side by means of the ECU
20.
Seventh Embodiment
[0179] Next, a seventh embodiment of the present invention will be
described with reference to FIG. 13. Here, a construction different
from that of the above-mentioned sixth embodiment will be
described, and an explanation of the same construction will be
omitted.
[0180] The difference of this seventh embodiment from the
above-mentioned sixth embodiment is that in cases where acid
neutralization processing is carried out during the execution of
deceleration fuel cut-off control, the exhaust throttle valve 27 is
caused to close.
[0181] In the following, an execution procedure of the acid
neutralization processing in this embodiment will be described
refer to FIG. 13. FIG. 13 is a flow chart showing a control routine
which is executed by the ECU 20 at the time when the acid
neutralization processing is carried out in this embodiment. Here,
note that in FIG. 13, the same symbols are attached to the same
processes as those in the above-mentioned control routine of the
sixth embodiment (see FIG. 12).
[0182] In the control routine of FIG. 13, in cases where an
affirmative determination is made in step S301, the ECU 20 carries
out the processing of steps S601 through S603 before the execution
of the processing of step S302. First, in step S601, the ECU 20
determines whether deceleration fuel cut-off control is being
carried out.
[0183] In cases where an affirmative determination is made in the
above-mentioned step S601, the process of the ECU 20 goes to step
S602, in which the second throttle valve 19 and the exhaust
throttle valve 27 are caused to close, and at the same time, the
low pressure EGR valve 17 is caused to open. When the acid
neutralization processing is carried out in such a state, all of
the ammonia (NH.sub.3) having flowed out of the selective reduction
type catalyst 26 will flow into the low pressure EGR passage 16. In
other words, all of the ammonia (NH.sub.3) having flowed out of the
selective reduction type catalyst 26 can be used as a neutralizing
agent. As a result, the acidic substances can be neutralized, while
suppressing the amount of consumption of the urea aqueous solution
accompanying the execution of the acid neutralization processing to
a small level.
[0184] In addition, in cases where a negative determination is made
in the above-mentioned step S601, the process of the ECU 20 goes to
step S603, in which the degrees of opening of the second throttle
valve 19, the exhaust throttle valve 27 and the low pressure EGR
valve 17 are controlled to their ordinary degrees of opening,
respectively.
[0185] Here, note that in this embodiment, reference has been made
to an example in which acid neutralization processing is carried
out even at the time of non-execution of deceleration fuel cut-off
control, but acid neutralization processing may be carried out only
at the time of execution of deceleration fuel cut-off control. In
that case, it is possible to suppress the amount of consumption of
the urea aqueous solution accompanying the execution of the acid
neutralization processing to a much smaller level.
Eighth Embodiment
[0186] Next, a eighth embodiment of the present invention will be
described with reference to FIG. 14. Here, a construction different
from that of the above-mentioned first embodiment will be
described, and an explanation of the same construction will be
omitted.
[0187] The difference of this eighth embodiment from the
above-mentioned first embodiment is that the amount of the urea
aqueous solution to be supplied from the addition valve 25 is
regulated (corrected) according to the amount of low pressure EGR
gas at the time of the execution of acid neutralization
processing.
[0188] In case where acid neutralization processing is carried out
in the construction in which the selective reduction type catalyst
26 is arranged in a portion of the exhaust passage 6 at the
downstream side of the connection portion of the low pressure EGR
passage 16, a part of the urea aqueous solution added from the
addition valve 25 will flow into the low pressure EGR passage 16,
and the remaining urea aqueous solution will flow into the
selective reduction type catalyst 26.
[0189] In that case, the amount of the urea aqueous solution (the
amount of ammonia) flowing into the selective reduction type
catalyst 26 changes in accordance with the amount of the low
pressure EGR gas. That is, the amount of the urea aqueous solution
flowing into the selective reduction type catalyst 26 becomes
smaller in comparison with the time when the amount of the low
pressure EGR gas is small. If the amount of the urea aqueous
solution flowing into the selective reduction type catalyst 26
becomes excessively smaller, it will be a possibility that the
selective reduction type catalyst 26 becomes unable to remove the
nitrogen oxides (NOx) in the exhaust gas in an effective or
practical manner.
[0190] On the other hand, in the acid neutralization processing of
this embodiment, when the amount of the low pressure EGR gas is
large, the amount of the urea aqueous solution supplied from the
addition valve 25 is made to become larger in comparison with the
time when the amount of the low pressure EGR gas is small.
According to such a method, even in cases where the urea aqueous
solution is supplied from the addition valve 25 at the time of the
execution of the acid neutralization processing (at the time of the
opening of the low pressure EGR valve 17), it becomes possible to
supply a necessary amount of ammonia (NH.sub.3) to the selective
reduction type catalyst 26.
[0191] In the following, an execution procedure of the acid
neutralization processing in this embodiment will be described
refer to FIG. 14. FIG. 14 is a flow chart showing a control routine
which is executed by the ECU 20 at the time when the acid
neutralization processing is carried out. In FIG. 14, the same
symbols are attached to the same processes as those in the
above-mentioned control routine of the first embodiment (see FIG.
2).
[0192] In the control routine of FIG. 14, in cases where an
affirmative determination is made in step S101, the ECU 20 carries
out the processing of step S701. In step S701, the ECU 20
calculates the amount anhscr of the ammonia (NH.sub.3) supplied to
the selective reduction type catalyst 26, in cases where it is
assumed that a predetermined amount of urea aqueous solution has
been added to the exhaust gas from the addition valve 25. The
predetermined amount referred to herein may be a fixed amount which
has been beforehand set, or may be a variable amount which is
decided by using, as a parameter, the amount or hydrogen ion
exponent (pH) of the acidic substances existing in the path of the
low pressure EGR gas.
[0193] In calculating the amount anhscr of the ammonia (NH.sub.3)
supplied to the selective reduction type catalyst 26, the ECU 20
first calculates the concentration of ammonia (NH.sub.3) contained
in the exhaust gas by using, as parameters, an amount of the urea
aqueous solution to be supplied from the addition valve 25 and a
flow rate (amount) Gex of the exhaust gas. Subsequently, the ECU 20
obtains the amount of the exhaust gas flowing from the exhaust
passage 6 into the low pressure EGR passage 16, i.e., the amount of
low pressure EGR gas G1pl. The amount of low pressure EGR gas G1pl
can be obtained by means of a map or a computational model which
uses, as arguments, the operational condition (the amount of intake
air, the number of engine revolutions per unit time, etc.) of the
internal combustion engine 1, the degree of opening of the low
pressure EGR valve 17, the degree of opening of the exhaust
throttle valve 27, and so on.
[0194] The ECU 20 calculates an amount Gscr of the exhaust gas
flowing into the selective reduction type catalyst 26 (=Gex-G1pl)
by subtracting the amount of low pressure EGR gas G1pl from the
flow rate (amount) of the exhaust gas Gex. The ECU 20 calculates
the amount anhscr (=Cnh3rl*Gscr) of the ammonia (NH.sub.3) supplied
to the selective reduction type catalyst 26 by multiplying the
amount Gscr of the exhaust gas flowing into the selective reduction
type catalyst 26 and the concentration Cnh3rl of ammonia
(NH.sub.3).
[0195] When the amount anhscr of the ammonia (NH.sub.3) supplied to
the selective reduction type catalyst 26 is calculated according to
the method as referred to above, the process of the ECU 20 goes to
step S702. In step S702, the ECU 20 determines whether the
difference between the amount of supply anhscr of ammonia
(NH.sub.3) obtained in the above-mentioned step S701 and a target
value anhtrg of the amount of adsorption of ammonia is not more
than a permissible value.
[0196] In cases where an affirmative determination is made in the
above-mentioned step S702, the process of the ECU 20 goes to step
S102, in which a predetermined amount of urea aqueous solution is
caused to be supplied from the addition valve 25. On the other
hand, in cases where a negative determination is made in the
above-mentioned step S702, the process of the ECU 20 goes to step
S703, in which the above-mentioned predetermined amount is
corrected. Specifically, in cases where the above-mentioned amount
of supply anhscr is less than the above-mentioned target value
anhtrg, the ECU 20 corrects the above-mentioned predetermined
amount in an increasing direction. On the other hand, in cases
where the above-mentioned amount of supply anhscr is larger than
the above-mentioned target value anhtrg, the ECU 20 corrects the
above-mentioned predetermined amount in a decreasing direction.
[0197] After carrying out the above-mentioned processing of step
S703, the process of the ECU 20 goes to step S102, and operates the
addition valve 25 in accordance with the predetermined amount
corrected in the above-mentioned step S703.
[0198] According to the embodiment described above, it is possible
to carry out the acid neutralization processing, without decreasing
the purification ability of the selective reduction type catalyst
26. As a result, it is possible to neutralize the acidic substances
in the low pressure EGR gas passage, without increasing harmful
exhaust emissions of the internal combustion engine 1.
Ninth Embodiment
[0199] Next, a ninth embodiment of the present invention will be
described with reference to FIG. 15. Here, a construction different
from that of the above-mentioned first embodiment will be
described, and an explanation of the same construction will be
omitted.
[0200] The difference of this ninth embodiment from the
above-mentioned first embodiment is that the flow rate ratio of the
low pressure EGR gas and the high pressure EGR gas is regulated in
accordance with the amount of the ammonia (NH.sub.3) flowing into
the low pressure EGR passage 16 at the time when acid
neutralization processing is carried out.
[0201] It can be assumed that when the flow rate of the low
pressure EGR gas is small, or when the flow rate of the low
pressure EGR gas is zero (only a high pressure EGR mechanism is in
operation), it becomes difficult to supply an amount of ammonia
(NH.sub.3) corresponding to the amount of the acidic substances
existing in the path of the low pressure EGR gas to the path of the
low pressure EGR gas.
[0202] On the other hand, it can also be assumed that when the flow
rate of the low pressure EGR gas is large, or when only the low
pressure EGR gas operates (the amount of high pressure EGR gas
becomes zero), the amount of supply of ammonia (NH.sub.3) will
become excessive with respect to the amount of the acidic
substances existing in the path of the low pressure EGR gas. In
particular, in the construction in which the selective reduction
type catalyst 26 is arranged in a portion of the exhaust passage 6
at the downstream side of the connection portion of the low
pressure EGR passage 16, when a desired amount of ammonia
(NH.sub.3) is to be supplied to the selective reduction type
catalyst 26, there is a high possibility that the amount of the
ammonia (NH.sub.3) supplied to the low pressure EGR passage 16 may
become excessive.
[0203] On the other hand, in the acid neutralization processing of
this embodiment, when the amount of the ammonia (NH.sub.3) supplied
to the low pressure EGR passage 16 is insufficient, the ECU 20
serves to make an increase correction of the flow rate ratio of the
low pressure EGR gas with respect to the high pressure EGR gas. In
that case, the amount of the ammonia (NH.sub.3) supplied to the
path of the low pressure EGR gas can be made to increase, without
changing the amount of EGR gas (i.e., the total amount of the
amount of low pressure EGR gas and the amount of high pressure EGR
gas) introduced into the internal combustion engine 1.
[0204] On the other hand, when the amount of the ammonia (NH.sub.3)
supplied to the low pressure EGR passage 16 is excessive, the ECU
20 serves to make a decrease correction of the flow rate ratio of
the low pressure EGR gas with respect to the high pressure EGR gas.
In that case, the amount of the ammonia (NH.sub.3) supplied to the
path of the low pressure EGR gas can be made to decrease, without
changing the amount of EGR gas introduced into the internal
combustion engine 1.
[0205] In the following, an execution procedure of the acid
neutralization processing in this embodiment will be described
refer to FIG. 15. FIG. 15 is a flow chart showing a subroutine
which the ECU 20 carries out during or before the execution of the
acid neutralization processing.
[0206] In the subroutine of FIG. 15, first in step S801, the ECU 20
calculates a ratio .alpha. (=(the amount of low pressure EGR
gas)/(the total amount of EGR gas)) of the amount of low pressure
EGR gas with respect to the total amount of EGR gas (the total sum
of the amount of high pressure EGR gas and the amount of low
pressure EGR gas).
[0207] In step S802, the ECU 20 calculates the amount Gac of the
acidic substances existing in the path of the low pressure EGR gas.
The amount Gac of acidic substances can be obtained according to
the same method as in the above-mentioned fourth embodiment.
[0208] In step S803, the ECU 20 calculates an amount Ghn31pl of the
ammonia (NH.sub.3) flowing into the low pressure EGR passage 16
based on the ratio .alpha. thus calculated in the above-mentioned
step S801. Here, note that in cases where the subroutine of FIG. 15
is carried out before the execution of the acid neutralization
processing, the ECU 20 carries out the above-mentioned calculation
on the assumption that a predetermined amount of urea aqueous
solution has been added from the addition valve 25.
[0209] In step S804, the ECU 20 calculates a difference .DELTA.G
(=Ghn31pl-Gac) between the amount Gac of the acidic substances
calculated in the above-mentioned step S802 and the amount Ghn31pl
of the ammonia (NH.sub.3) calculated in the above-mentioned step
S803.
[0210] In step S805, the ECU 20 calculates an amount of correction
.DELTA.C for correcting the ratio .alpha. of the amount of low
pressure EGR gas with respect to the total amount of EGR gas. The
amount of correction .DELTA.C may be a fixed amount which has been
beforehand set, or may be a variable amount which is set to be a
larger value when an absolute value of the difference .DELTA.G
calculated in the above-mentioned step S804 is large, in comparison
with the time when it is small.
[0211] In step S806, the ECU 20 determines whether the difference
.DELTA.G calculated in the above-mentioned step S804 is larger than
zero. In cases where an affirmative determination is made in step
S806 (.DELTA.G>0), the ECU 20 goes to step S807. In step S807,
when the ECU 20 makes a decrease correction of the ratio .alpha. of
the amount of low pressure EGR gas with respect to the total amount
of EGR gas by subtracting the above-mentioned amount of correction
.DELTA.C from the ratio .alpha. obtained in the above-mentioned
step S801. In that case, the amount of high pressure EGR gas is
increased, and at the same time, the amount of low pressure EGR gas
is decreased. As a result, the amount of the ammonia (NH.sub.3)
supplied to the low pressure EGR passage 16 decreases, without the
total amount of EGR gas being changed.
[0212] On the other hand, in cases where a negative determination
is made in the above-mentioned step S806 (.DELTA.G.ltoreq.0), the
process of the ECU 20 goes to step S808, in which it is determined
whether the above-mentioned difference .DELTA.G is smaller than
zero. In cases where an affirmative determination is made in step
S808 (.DELTA.G<0), the ECU 20 goes to step S809. In step S809,
when the ECU 20 makes an increase correction of the ratio .alpha.
of the amount of low pressure EGR gas with respect to the total
amount of EGR gas by adding the above-mentioned amount of
correction .DELTA.C to the ratio .alpha. obtained in the
above-mentioned step S801. In that case, the amount of high
pressure EGR gas is decreased, and at the same time, the amount of
low pressure EGR gas is increased. As a result, the amount of the
ammonia (NH.sub.3) supplied to the low pressure EGR passage 16
increases, without the total amount of EGR gas being changed.
[0213] Here, note that in cases where a negative determination is
made in the above-mentioned step S808 (.DELTA.G=0), the ECU 20 once
terminates the execution of this routine.
[0214] According to the embodiment described above, even in cases
where a low pressure EGR mechanism is in a non-operating state
(i.e., in cases where the low pressure EGR valve 17 is in a valve
dosed state), or in cases where the flow rate ratio of the amount
of low pressure EGR gas with respect to the amount of high pressure
EGR gas is low, it becomes possible to neutralize the acidic
substances in the path of the low pressure EGR gas.
[0215] However, it can be assumed that when the ratio .alpha. of
the amount of low pressure EGR gas is increased in an operation
region where only the high pressure EGR mechanism operates, or in
an operation region where both of the high pressure EGR mechanism
and the low pressure EGR mechanism operate, a misfire will occur
due to a drop in the temperature at a compression end.
[0216] Accordingly, on the condition that the temperature of the
gas introduced into each of the combustion chambers of the internal
combustion engine 1 is higher than a lower limit value thereof, the
ratio .alpha. of the amount of low pressure EGR gas may be
corrected in an increasing direction. In that case, the ECU 20
should just correct the ratio .alpha. of the amount of low pressure
EGR gas according to a subroutine as shown in FIG. 16.
[0217] The difference of the subroutine in FIG. 16 from the
subroutine in FIG. 15 is that in cases where an affirmative
determination is made in S808 (.DELTA.G<0), the processing of
step S901 is carried out. In step S901, the ECU 20 determines
whether the temperature Tin of the gas introduced into each of the
combustion chambers of the internal combustion engine 1 is not less
than a lower limit temperature Tinlt.
[0218] Here, as the temperature Tin of the gas introduced into the
combustion chamber of the internal combustion engine 1, there can
be used the temperature of the gas in a portion of the intake
passage 4 at the downstream side of the connection portion of the
high pressure EGR passage 12 (e.g., the temperature in the intake
manifold 5). The temperature in the intake manifold 5 may be
measured by a temperature sensor. In addition, the temperature in
the intake manifold 5 may be obtained by making use of a map or a
computational model which uses, as arguments, the amount of intake
air, the temperature of intake air, the amount of the high pressure
EGR gas, the temperature of the high pressure EGR gas, the amount
of the low pressure EGR gas, the temperature of the low pressure
EGR gas, and so on.
[0219] The above-mentioned lower limit temperature Tinlt is the
lowest temperature of a temperature range in which a misfire can
not occur, or a temperature which is a little higher than the
above-mentioned lowest temperature, and it has been beforehand set
by adaptation or calibration work making use of experiments,
etc.
[0220] In cases where an affirmative determination is made in the
above-mentioned step S901 (Tin.gtoreq.Tinlt), the ECU 20 goes to
step S809, in which an increase correction of the ratio .alpha. of
the amount of low pressure EGR gas is carried out. However, in
cases where a negative determination is made in the above-mentioned
step S901 (Tin<Tinlt), the execution of this routine is ended,
without the ratio .alpha. of the amount of low pressure EGR gas
being corrected.
[0221] According to the subroutine as shown in FIG. 16, only in
cases where the occurrence of a misfire can be avoided, the ratio
.alpha. of the amount of low pressure EGR gas will be corrected in
an increasing direction. As a result, it is possible to avoid
reduction in drivability of the internal combustion engine 1
resulting from the execution of the acid neutralization
processing.
[0222] Here, note that in cases where a negative determination is
made in the above-mentioned step S901 (Tin<Tinlt), the increase
correction of the ratio .alpha. may be carried out, while
performing control in such a manner that the low pressure EGR gas
flows so as to bypass the low pressure EGR cooler 18, or the high
pressure EGR gas flows so as to bypass the high pressure EGR cooler
14. In addition, the increase correction of the ratio .alpha. may
be carried out, while causing the temperatures of the low pressure
EGR gas and the high pressure EGR gas to rise by adjusting the
timing of fuel injection.
[0223] On the other hand, it can be assumed that in the operation
region where only the low pressure EGR mechanism operates, or in
the operation region where both of the high pressure EGR mechanism
and the low pressure EGR mechanism operate, when the ratio .alpha.
of the amount of low pressure EGR gas is decreased (i.e., the
amount of high pressure EGR gas is increased), the component parts
(e.g., the high pressure EGR valve 13, etc.) inside the path of the
high pressure EGR gas will be overheated, or preignition of fuel
will occur due to a rise in the temperature at the compression
end.
[0224] Accordingly, on the condition that the temperature of the
high pressure EGR gas is lower than an upper limit value thereof,
the ratio .alpha. of the amount of low pressure EGR gas may be
corrected in a decreasing direction. In that case, the ECU 20
should just correct the ratio .alpha. of the amount of low pressure
EGR gas according to a subroutine as shown in FIG. 17.
[0225] The difference of the subroutine in FIG. 17 from the
subroutine in FIG. 15 is that in cases where an affirmative
determination is made in S806 (.DELTA.G>0), the processing of
step S1001 is carried out. In step S1001, the ECU 20 determines
whether the temperature Thv of the high pressure EGR gas is not
more than an upper limit temperature Thvlt.
[0226] Here, as the temperature Thv of the high pressure EGR gas,
there can be used the temperature of the high pressure EGR gas in
the vicinity of the high pressure EGR valve 13. The temperature of
the high pressure EGR gas in the vicinity of the high pressure EGR
valve 13 may be measured by a temperature sensor, or may be
calculated from an operating state of the internal combustion
engine 1 (the number of engine revolutions per unit time, the
amount of fuel injection, or the like).
[0227] The above-mentioned upper limit temperature Thvlt is the
lower of either the highest temperature of a temperature range in
which the high pressure EGR valve 13 or the like does not overheat,
or the highest temperature of a temperature range in which
preignition of fuel can be avoided, or is a temperature which is a
little lower than that temperature. The upper limit temperature
Thvlt has been beforehand set by adaptation or calibration work
making use of experiments, etc.
[0228] In cases where an affirmative determination is made in the
above-mentioned step S1001 (Thv.ltoreq.Thvlt), the ECU 20 goes to
step S807, in which a decrease correction of the ratio c of the
amount of low pressure EGR gas is carried out. However, in cases
where a negative determination is made in the above-mentioned step
S1001 (Thv>Thvlt), the execution of this routine is ended,
without the ratio .alpha. of the amount of low pressure EGR gas
being corrected.
[0229] According to the subroutine as shown in FIG. 17, only in
cases where overheating of those component parts which are arranged
in the path of the high pressure EGR gas, or preignition of fuel
can be avoided, the ratio .alpha. of the amount of low pressure EGR
gas will be corrected in a decreasing direction. As a result, it is
possible to avoid deterioration in the component parts and
reduction in drivability of the internal combustion engine 1
resulting from the execution of the acid neutralization
processing.
[0230] Here, note that in cases where a negative determination is
made in the above-mentioned step S1001 (Thv>Thclt), the decrease
correction of the ratio .alpha. may be carried out, while
increasing the amount of the low pressure EGR gas flowing by way of
the low pressure EGR cooler 18, or increasing the amount of the
high pressure EGR gas flowing by way of the high pressure EGR
cooler 14. In addition, the decrease correction of the ratio
.alpha. may be carried out, while causing the temperatures of the
low pressure EGR gas and the high pressure EGR gas to drop by
adjusting the timing of fuel injection.
[0231] Here, note that in the above-mentioned first, second, and
fourth through eighth embodiments, reference has been made to
examples in which the present invention is applied to an internal
combustion engine having a low pressure EGR mechanism and a high
pressure EGR mechanism, but it is also possible to apply the
present invention to an internal combustion engine which is not
provided with a high pressure EGR mechanism.
DESCRIPTION OF THE REFERENCE NUMERALS AND SYMBOLS
[0232] 1 internal combustion engine [0233] 2 cylinder(s) [0234] 3
fuel injection valve [0235] 4 intake passage [0236] 5 intake
manifold [0237] 6 exhaust passage [0238] 7 exhaust manifold [0239]
8 turbocharger [0240] 8a compressor [0241] 8b turbine [0242] 9
first throttle valve [0243] 11 high pressure EGR device [0244] 12
high pressure EGR passage [0245] 13 high pressure EGR valve [0246]
14 high pressure EGR cooler [0247] 15 low pressure EGR device
[0248] 16 low pressure EGR passage [0249] 17 low pressure EGR valve
[0250] 18 low pressure EGR cooler [0251] 19 second throttle valve
[0252] 21 crank position sensor [0253] 22 accelerator position
sensor [0254] 23 oxidation catalyst [0255] 24 particulate filter
[0256] 25 addition valve [0257] 26 selective reduction type
catalyst [0258] 27 exhaust throttle valve [0259] 28 exhaust gas
temperature sensor [0260] 29 dispersion plate [0261] 30 hydrolysis
catalyst [0262] 40 intercooler [0263] 260 heater
* * * * *